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 $92.27   10.753%   $102.1918   $102.19   $102.20   $102.20  
  Purchase #2 $164.87   5.206%   $173.4531   $173.45   $173.45   $173.50  
  Purchase #3 $196.96   9.347%   $215.3699   $215.37   $215.35   $215.40  
  Purchase #4 $67.40   13.590%   $76.5597   $76.56   $76.55   $76.60  
  Purchase #5 $151.34   11.539%   $168.8031   $168.80   $168.80   $168.80  
  Purchase #6 $123.76   4.514%   $129.3465   $129.35   $129.35   $129.30  
  Purchase #7 $126.40   9.145%   $137.9593   $137.96   $137.95   $138.00  
  7 purchase totals = $923.00       $1,003.6834   $1,003.68   $1,003.65   $1,003.80