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 $212.44   11.557%   $236.9917   $236.99   $237.00   $237.00  
  Purchase #2 $58.32   7.523%   $62.7074   $62.71   $62.70   $62.70  
  Purchase #3 $115.60   13.111%   $130.7563   $130.76   $130.75   $130.80  
  Purchase #4 $44.31   6.334%   $47.1166   $47.12   $47.10   $47.10  
  Purchase #5 $234.71   5.810%   $248.3467   $248.35   $248.35   $248.30  
  Purchase #6 $54.52   11.281%   $60.6704   $60.67   $60.65   $60.70  
  Purchase #7 $17.93   12.776%   $20.2207   $20.22   $20.20   $20.20  
  7 purchase totals = $737.83       $806.8098   $806.82   $806.75   $806.80