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 $174.44   7.110%   $186.8427   $186.84   $186.85   $186.80  
  Purchase #2 $207.97   12.682%   $234.3448   $234.34   $234.35   $234.30  
  Purchase #3 $95.93   9.322%   $104.8726   $104.87   $104.85   $104.90  
  Purchase #4 $200.47   3.141%   $206.7668   $206.77   $206.75   $206.80  
  Purchase #5 $62.46   10.491%   $69.0127   $69.01   $69.00   $69.00  
  Purchase #6 $63.73   3.556%   $65.9962   $66.00   $66.00   $66.00  
  Purchase #7 $74.61   11.411%   $83.1237   $83.12   $83.10   $83.10  
  7 purchase totals = $879.61       $950.9595   $950.95   $950.90   $950.90