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 $206.76   10.824%   $229.1397   $229.14   $229.15   $229.10  
  Purchase #2 $112.77   9.374%   $123.3411   $123.34   $123.35   $123.30  
  Purchase #3 $45.89   5.362%   $48.3506   $48.35   $48.35   $48.40  
  Purchase #4 $193.79   4.106%   $201.747   $201.75   $201.75   $201.70  
  Purchase #5 $123.52   5.831%   $130.7225   $130.72   $130.70   $130.70  
  Purchase #6 $147.40   3.377%   $152.3777   $152.38   $152.40   $152.40  
  Purchase #7 $64.69   4.116%   $67.3526   $67.35   $67.35   $67.40  
  7 purchase totals = $894.82       $953.0312   $953.03   $953.05   $953.00