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 $34.70   8.230%   $37.5558   $37.56   $37.55   $37.60  
  Purchase #2 $91.92   10.645%   $101.7049   $101.70   $101.70   $101.70  
  Purchase #3 $220.66   5.316%   $232.3903   $232.39   $232.40   $232.40  
  Purchase #4 $234.90   3.323%   $242.7057   $242.71   $242.70   $242.70  
  Purchase #5 $146.36   7.610%   $157.498   $157.50   $157.50   $157.50  
  Purchase #6 $13.45   6.630%   $14.3417   $14.34   $14.35   $14.30  
  Purchase #7 $223.54   10.666%   $247.3828   $247.38   $247.40   $247.40  
  7 purchase totals = $965.53       $1,033.5792   $1,033.58   $1,033.60   $1,033.60