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 $67.43   6.277%   $71.6626   $71.66   $71.65   $71.70  
  Purchase #2 $221.65   13.330%   $251.1959   $251.20   $251.20   $251.20  
  Purchase #3 $236.71   12.562%   $266.4455   $266.45   $266.45   $266.40  
  Purchase #4 $24.35   5.485%   $25.6856   $25.69   $25.70   $25.70  
  Purchase #5 $202.49   7.102%   $216.8708   $216.87   $216.85   $216.90  
  Purchase #6 $45.92   7.802%   $49.5027   $49.50   $49.50   $49.50  
  Purchase #7 $232.55   8.443%   $252.1842   $252.18   $252.20   $252.20  
  7 purchase totals = $1,031.10       $1,133.5473   $1,133.55   $1,133.55   $1,133.60