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 $64.91   7.335%   $69.6711   $69.67   $69.65   $69.70  
  Purchase #2 $132.74   4.223%   $138.3456   $138.35   $138.35   $138.30  
  Purchase #3 $222.65   4.441%   $232.5379   $232.54   $232.55   $232.50  
  Purchase #4 $238.58   4.399%   $249.0751   $249.08   $249.10   $249.10  
  Purchase #5 $99.80   12.681%   $112.4556   $112.46   $112.45   $112.50  
  Purchase #6 $51.28   7.259%   $55.0024   $55.00   $55.00   $55.00  
  Purchase #7 $86.41   9.308%   $94.453   $94.45   $94.45   $94.50  
  7 purchase totals = $896.37       $951.5407   $951.55   $951.55   $951.60