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 $194.26   10.828%   $215.2945   $215.29   $215.30   $215.30  
  Purchase #2 $89.77   11.783%   $100.3476   $100.35   $100.35   $100.30  
  Purchase #3 $244.43   9.291%   $267.14   $267.14   $267.15   $267.10  
  Purchase #4 $112.79   8.400%   $122.2644   $122.26   $122.25   $122.30  
  Purchase #5 $202.77   4.500%   $211.8947   $211.89   $211.90   $211.90  
  Purchase #6 $167.86   11.523%   $187.2025   $187.20   $187.20   $187.20  
  Purchase #7 $127.70   7.726%   $137.5661   $137.57   $137.55   $137.60  
  7 purchase totals = $1,139.58       $1,241.7098   $1,241.70   $1,241.70   $1,241.70