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 $232.27   12.256%   $260.737   $260.74   $260.75   $260.70  
  Purchase #2 $206.89   12.397%   $232.5382   $232.54   $232.55   $232.50  
  Purchase #3 $36.88   6.518%   $39.2838   $39.28   $39.30   $39.30  
  Purchase #4 $56.54   9.766%   $62.0617   $62.06   $62.05   $62.10  
  Purchase #5 $75.67   9.474%   $82.839   $82.84   $82.85   $82.80  
  Purchase #6 $11.91   8.189%   $12.8853   $12.89   $12.90   $12.90  
  Purchase #7 $99.65   5.284%   $104.9155   $104.92   $104.90   $104.90  
  7 purchase totals = $719.81       $795.2605   $795.27   $795.30   $795.20