Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
  Case Tag  
Price  
Sales  
Tax %  
Raw Total  
Incl. Sales Tax  
Rounded  
to Penny  
Rounded  
to Nickel  
Rounded  
to Dime  
  Purchase #1 $194.69   13.139%   $220.2703   $220.27   $220.25   $220.30  
  Purchase #2 $154.41   11.755%   $172.5609   $172.56   $172.55   $172.60  
  Purchase #3 $98.88   6.145%   $104.9562   $104.96   $104.95   $105.00  
  Purchase #4 $107.77   7.595%   $115.9551   $115.96   $115.95   $116.00  
  Purchase #5 $247.89   3.238%   $255.9167   $255.92   $255.90   $255.90  
  Purchase #6 $223.27   10.501%   $246.7156   $246.72   $246.70   $246.70  
  Purchase #7 $225.40   11.726%   $251.8304   $251.83   $251.85   $251.80  
  7 purchase totals = $1,252.31       $1,368.2052   $1,368.22   $1,368.15   $1,368.30