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 $188.56   12.672%   $212.4543   $212.45   $212.45   $212.50  
  Purchase #2 $51.74   6.305%   $55.0022   $55.00   $55.00   $55.00  
  Purchase #3 $88.60   9.193%   $96.745   $96.75   $96.75   $96.70  
  Purchase #4 $60.85   3.404%   $62.9213   $62.92   $62.90   $62.90  
  Purchase #5 $211.38   3.464%   $218.7022   $218.70   $218.70   $218.70  
  Purchase #6 $5.71   5.182%   $6.0059   $6.01   $6.00   $6.00  
  Purchase #7 $186.61   8.605%   $202.6678   $202.67   $202.65   $202.70  
  7 purchase totals = $793.45       $854.4987   $854.50   $854.45   $854.50