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 $82.41   12.319%   $92.5621   $92.56   $92.55   $92.60  
  Purchase #2 $58.99   10.799%   $65.3603   $65.36   $65.35   $65.40  
  Purchase #3 $85.79   10.579%   $94.8657   $94.87   $94.85   $94.90  
  Purchase #4 $201.82   5.381%   $212.6799   $212.68   $212.70   $212.70  
  Purchase #5 $40.34   11.255%   $44.8803   $44.88   $44.90   $44.90  
  Purchase #6 $100.88   13.257%   $114.2537   $114.25   $114.25   $114.30  
  Purchase #7 $166.98   6.831%   $178.3864   $178.39   $178.40   $178.40  
  7 purchase totals = $737.21       $802.9884   $802.99   $803.00   $803.20