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 $217.78   11.585%   $243.0098   $243.01   $243.00   $243.00  
  Purchase #2 $215.94   3.105%   $222.6449   $222.64   $222.65   $222.60  
  Purchase #3 $35.41   12.789%   $39.9386   $39.94   $39.95   $39.90  
  Purchase #4 $217.35   13.678%   $247.0791   $247.08   $247.10   $247.10  
  Purchase #5 $123.69   7.268%   $132.6798   $132.68   $132.70   $132.70  
  Purchase #6 $25.97   11.162%   $28.8688   $28.87   $28.85   $28.90  
  Purchase #7 $239.53   8.859%   $260.75   $260.75   $260.75   $260.80  
  7 purchase totals = $1,075.67       $1,174.9710   $1,174.97   $1,175.00   $1,175.00