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 $85.35   11.451%   $95.1234   $95.12   $95.10   $95.10  
  Purchase #2 $233.49   13.305%   $264.5558   $264.56   $264.55   $264.60  
  Purchase #3 $143.98   9.673%   $157.9072   $157.91   $157.90   $157.90  
  Purchase #4 $60.59   6.110%   $64.292   $64.29   $64.30   $64.30  
  Purchase #5 $98.56   6.354%   $104.8225   $104.82   $104.80   $104.80  
  Purchase #6 $176.96   9.234%   $193.3005   $193.30   $193.30   $193.30  
  Purchase #7 $75.54   8.198%   $81.7328   $81.73   $81.75   $81.70  
  7 purchase totals = $874.47       $961.7342   $961.73   $961.70   $961.70