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 $183.76   9.553%   $201.3146   $201.31   $201.30   $201.30  
  Purchase #2 $166.87   9.464%   $182.6626   $182.66   $182.65   $182.70  
  Purchase #3 $14.66   12.107%   $16.4349   $16.43   $16.45   $16.40  
  Purchase #4 $165.78   13.836%   $188.7173   $188.72   $188.70   $188.70  
  Purchase #5 $176.99   13.222%   $200.3916   $200.39   $200.40   $200.40  
  Purchase #6 $154.63   9.455%   $169.2503   $169.25   $169.25   $169.30  
  Purchase #7 $70.93   11.731%   $79.2508   $79.25   $79.25   $79.30  
  7 purchase totals = $933.62       $1,038.0221   $1,038.01   $1,038.00   $1,038.10