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 $176.82   12.826%   $199.4989   $199.50   $199.50   $199.50  
  Purchase #2 $133.88   4.521%   $139.9327   $139.93   $139.95   $139.90  
  Purchase #3 $48.25   5.174%   $50.7465   $50.75   $50.75   $50.70  
  Purchase #4 $59.48   5.209%   $62.5783   $62.58   $62.60   $62.60  
  Purchase #5 $122.31   9.747%   $134.2316   $134.23   $134.25   $134.20  
  Purchase #6 $211.72   11.207%   $235.4475   $235.45   $235.45   $235.40  
  Purchase #7 $103.52   10.403%   $114.2892   $114.29   $114.30   $114.30  
  7 purchase totals = $855.98       $936.7247   $936.73   $936.80   $936.60