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 $82.49   13.393%   $93.5379   $93.54   $93.55   $93.50  
  Purchase #2 $85.84   6.513%   $91.4308   $91.43   $91.45   $91.40  
  Purchase #3 $125.77   5.126%   $132.217   $132.22   $132.20   $132.20  
  Purchase #4 $234.65   6.393%   $249.6512   $249.65   $249.65   $249.70  
  Purchase #5 $248.46   9.174%   $271.2537   $271.25   $271.25   $271.30  
  Purchase #6 $70.46   9.328%   $77.0325   $77.03   $77.05   $77.00  
  Purchase #7 $188.91   12.594%   $212.7013   $212.70   $212.70   $212.70  
  7 purchase totals = $1,036.58       $1,127.8244   $1,127.82   $1,127.85   $1,127.80