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 $163.79   13.290%   $185.5577   $185.56   $185.55   $185.60  
  Purchase #2 $217.76   12.294%   $244.5314   $244.53   $244.55   $244.50  
  Purchase #3 $83.60   13.704%   $95.0565   $95.06   $95.05   $95.10  
  Purchase #4 $34.40   10.399%   $37.9773   $37.98   $38.00   $38.00  
  Purchase #5 $87.93   4.557%   $91.937   $91.94   $91.95   $91.90  
  Purchase #6 $240.70   10.635%   $266.2984   $266.30   $266.30   $266.30  
  Purchase #7 $31.71   12.372%   $35.6332   $35.63   $35.65   $35.60  
  7 purchase totals = $859.89       $956.9915   $957.00   $957.05   $957.00