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 $204.83   9.620%   $224.5346   $224.53   $224.55   $224.50  
  Purchase #2 $182.62   8.526%   $198.1902   $198.19   $198.20   $198.20  
  Purchase #3 $125.32   6.644%   $133.6463   $133.65   $133.65   $133.60  
  Purchase #4 $80.26   4.838%   $84.143   $84.14   $84.15   $84.10  
  Purchase #5 $246.51   4.772%   $258.2735   $258.27   $258.25   $258.30  
  Purchase #6 $167.44   5.688%   $176.964   $176.96   $176.95   $177.00  
  Purchase #7 $160.62   7.442%   $172.5733   $172.57   $172.55   $172.60  
  7 purchase totals = $1,167.60       $1,248.3249   $1,248.31   $1,248.30   $1,248.30