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 $226.83   4.756%   $237.618   $237.62   $237.60   $237.60  
  Purchase #2 $101.51   5.298%   $106.888   $106.89   $106.90   $106.90  
  Purchase #3 $127.46   4.321%   $132.9675   $132.97   $132.95   $133.00  
  Purchase #4 $62.66   11.160%   $69.6529   $69.65   $69.65   $69.70  
  Purchase #5 $139.42   5.517%   $147.1118   $147.11   $147.10   $147.10  
  Purchase #6 $28.47   4.135%   $29.6472   $29.65   $29.65   $29.60  
  Purchase #7 $224.73   12.368%   $252.5246   $252.52   $252.50   $252.50  
  7 purchase totals = $911.08       $976.4100   $976.41   $976.35   $976.40