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 $201.59   4.261%   $210.1797   $210.18   $210.20   $210.20  
  Purchase #2 $146.65   9.344%   $160.353   $160.35   $160.35   $160.40  
  Purchase #3 $189.82   8.499%   $205.9528   $205.95   $205.95   $206.00  
  Purchase #4 $232.82   11.582%   $259.7852   $259.79   $259.80   $259.80  
  Purchase #5 $95.97   6.220%   $101.9393   $101.94   $101.95   $101.90  
  Purchase #6 $150.58   5.547%   $158.9327   $158.93   $158.95   $158.90  
  Purchase #7 $153.51   10.630%   $169.8281   $169.83   $169.85   $169.80  
  7 purchase totals = $1,170.94       $1,266.9708   $1,266.97   $1,267.05   $1,267.00