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 $205.41   10.692%   $227.3724   $227.37   $227.35   $227.40  
  Purchase #2 $194.76   11.363%   $216.8906   $216.89   $216.90   $216.90  
  Purchase #3 $19.65   10.260%   $21.6661   $21.67   $21.65   $21.70  
  Purchase #4 $158.46   8.523%   $171.9655   $171.97   $171.95   $172.00  
  Purchase #5 $95.54   6.830%   $102.0654   $102.07   $102.05   $102.10  
  Purchase #6 $193.95   4.794%   $203.248   $203.25   $203.25   $203.20  
  Purchase #7 $107.39   11.718%   $119.974   $119.97   $119.95   $120.00  
  7 purchase totals = $975.16       $1,063.1820   $1,063.19   $1,063.10   $1,063.30