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 $83.27   11.635%   $92.9585   $92.96   $92.95   $93.00  
  Purchase #2 $33.61   10.855%   $37.2584   $37.26   $37.25   $37.30  
  Purchase #3 $110.71   13.651%   $125.823   $125.82   $125.80   $125.80  
  Purchase #4 $177.86   7.826%   $191.7793   $191.78   $191.80   $191.80  
  Purchase #5 $63.59   11.607%   $70.9709   $70.97   $70.95   $71.00  
  Purchase #6 $78.26   9.295%   $85.5343   $85.53   $85.55   $85.50  
  Purchase #7 $21.60   9.316%   $23.6123   $23.61   $23.60   $23.60  
  7 purchase totals = $568.90       $627.9367   $627.93   $627.90   $628.00