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 $201.62   11.172%   $224.145   $224.15   $224.15   $224.10  
  Purchase #2 $185.64   13.613%   $210.9112   $210.91   $210.90   $210.90  
  Purchase #3 $57.71   3.494%   $59.7264   $59.73   $59.75   $59.70  
  Purchase #4 $213.72   6.260%   $227.0989   $227.10   $227.10   $227.10  
  Purchase #5 $238.79   3.140%   $246.288   $246.29   $246.30   $246.30  
  Purchase #6 $63.76   3.646%   $66.0847   $66.08   $66.10   $66.10  
  Purchase #7 $136.80   8.708%   $148.7125   $148.71   $148.70   $148.70  
  7 purchase totals = $1,098.04       $1,182.9667   $1,182.97   $1,183.00   $1,182.90