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 $54.86   11.106%   $60.9528   $60.95   $60.95   $61.00  
  Purchase #2 $245.92   4.779%   $257.6725   $257.67   $257.65   $257.70  
  Purchase #3 $228.82   8.216%   $247.6199   $247.62   $247.60   $247.60  
  Purchase #4 $146.70   4.498%   $153.2986   $153.30   $153.30   $153.30  
  Purchase #5 $16.78   11.874%   $18.7725   $18.77   $18.75   $18.80  
  Purchase #6 $28.34   12.609%   $31.9134   $31.91   $31.90   $31.90  
  Purchase #7 $110.82   12.478%   $124.6481   $124.65   $124.65   $124.60  
  7 purchase totals = $832.24       $894.8778   $894.87   $894.80   $894.90