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 $84.85   10.567%   $93.8161   $93.82   $93.80   $93.80  
  Purchase #2 $62.56   4.589%   $65.4309   $65.43   $65.45   $65.40  
  Purchase #3 $112.40   12.618%   $126.5826   $126.58   $126.60   $126.60  
  Purchase #4 $197.97   12.471%   $222.6588   $222.66   $222.65   $222.70  
  Purchase #5 $44.75   6.552%   $47.682   $47.68   $47.70   $47.70  
  Purchase #6 $216.55   11.437%   $241.3168   $241.32   $241.30   $241.30  
  Purchase #7 $81.54   4.471%   $85.1857   $85.19   $85.20   $85.20  
  7 purchase totals = $800.62       $882.6729   $882.68   $882.70   $882.70