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 $188.86   6.470%   $201.0792   $201.08   $201.10   $201.10  
  Purchase #2 $234.77   11.355%   $261.4281   $261.43   $261.45   $261.40  
  Purchase #3 $84.55   13.197%   $95.7081   $95.71   $95.70   $95.70  
  Purchase #4 $139.71   4.648%   $146.2037   $146.20   $146.20   $146.20  
  Purchase #5 $78.95   6.704%   $84.2428   $84.24   $84.25   $84.20  
  Purchase #6 $223.32   5.128%   $234.7718   $234.77   $234.75   $234.80  
  Purchase #7 $48.56   4.317%   $50.6563   $50.66   $50.65   $50.70  
  7 purchase totals = $998.72       $1,074.0900   $1,074.09   $1,074.10   $1,074.10