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 $205.94   13.612%   $233.9726   $233.97   $233.95   $234.00  
  Purchase #2 $24.73   6.667%   $26.3787   $26.38   $26.40   $26.40  
  Purchase #3 $169.67   4.441%   $177.205   $177.21   $177.20   $177.20  
  Purchase #4 $53.74   10.209%   $59.2263   $59.23   $59.25   $59.20  
  Purchase #5 $71.58   4.412%   $74.7381   $74.74   $74.75   $74.70  
  Purchase #6 $157.56   11.112%   $175.0681   $175.07   $175.05   $175.10  
  Purchase #7 $247.35   5.136%   $260.0539   $260.05   $260.05   $260.10  
  7 purchase totals = $930.57       $1,006.6427   $1,006.65   $1,006.65   $1,006.70