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 $54.39   11.436%   $60.61   $60.61   $60.60   $60.60  
  Purchase #2 $229.42   3.229%   $236.828   $236.83   $236.85   $236.80  
  Purchase #3 $59.95   4.757%   $62.8018   $62.80   $62.80   $62.80  
  Purchase #4 $214.36   10.244%   $236.319   $236.32   $236.30   $236.30  
  Purchase #5 $90.52   5.467%   $95.4687   $95.47   $95.45   $95.50  
  Purchase #6 $104.61   3.200%   $107.9575   $107.96   $107.95   $108.00  
  Purchase #7 $122.66   12.406%   $137.8772   $137.88   $137.90   $137.90  
  7 purchase totals = $875.91       $937.8622   $937.87   $937.85   $937.90