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 $210.86   3.698%   $218.6576   $218.66   $218.65   $218.70  
  Purchase #2 $148.43   8.805%   $161.4993   $161.50   $161.50   $161.50  
  Purchase #3 $227.35   4.216%   $236.9351   $236.94   $236.95   $236.90  
  Purchase #4 $97.65   8.843%   $106.2852   $106.29   $106.30   $106.30  
  Purchase #5 $143.38   12.861%   $161.8201   $161.82   $161.80   $161.80  
  Purchase #6 $219.39   12.338%   $246.4583   $246.46   $246.45   $246.50  
  Purchase #7 $241.58   7.860%   $260.5682   $260.57   $260.55   $260.60  
  7 purchase totals = $1,288.64       $1,392.2238   $1,392.24   $1,392.20   $1,392.30