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 $30.66   6.749%   $32.7292   $32.73   $32.75   $32.70  
  Purchase #2 $58.78   13.378%   $66.6436   $66.64   $66.65   $66.60  
  Purchase #3 $247.34   5.483%   $260.9017   $260.90   $260.90   $260.90  
  Purchase #4 $182.96   13.436%   $207.5425   $207.54   $207.55   $207.50  
  Purchase #5 $188.53   7.106%   $201.9269   $201.93   $201.95   $201.90  
  Purchase #6 $81.25   12.435%   $91.3534   $91.35   $91.35   $91.40  
  Purchase #7 $137.45   5.840%   $145.4771   $145.48   $145.50   $145.50  
  7 purchase totals = $926.97       $1,006.5744   $1,006.57   $1,006.65   $1,006.50