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 $44.88   4.170%   $46.7515   $46.75   $46.75   $46.80  
  Purchase #2 $182.75   11.791%   $204.2981   $204.30   $204.30   $204.30  
  Purchase #3 $219.51   9.576%   $240.5303   $240.53   $240.55   $240.50  
  Purchase #4 $16.69   6.124%   $17.7121   $17.71   $17.70   $17.70  
  Purchase #5 $29.50   5.783%   $31.206   $31.21   $31.20   $31.20  
  Purchase #6 $151.68   8.102%   $163.9691   $163.97   $163.95   $164.00  
  Purchase #7 $67.42   7.651%   $72.5783   $72.58   $72.60   $72.60  
  7 purchase totals = $712.43       $777.0454   $777.05   $777.05   $777.10