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 $34.39   10.610%   $38.0388   $38.04   $38.05   $38.00  
  Purchase #2 $234.53   11.864%   $262.3546   $262.35   $262.35   $262.40  
  Purchase #3 $204.68   13.133%   $231.5606   $231.56   $231.55   $231.60  
  Purchase #4 $53.74   8.306%   $58.2036   $58.20   $58.20   $58.20  
  Purchase #5 $170.93   11.244%   $190.1494   $190.15   $190.15   $190.10  
  Purchase #6 $244.99   13.536%   $278.1518   $278.15   $278.15   $278.20  
  Purchase #7 $15.61   13.556%   $17.7261   $17.73   $17.75   $17.70  
  7 purchase totals = $958.87       $1,076.1849   $1,076.18   $1,076.20   $1,076.20