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 $213.81   12.689%   $240.9404   $240.94   $240.95   $240.90  
  Purchase #2 $226.96   11.671%   $253.4485   $253.45   $253.45   $253.40  
  Purchase #3 $84.92   13.192%   $96.1226   $96.12   $96.10   $96.10  
  Purchase #4 $92.78   9.829%   $101.8993   $101.90   $101.90   $101.90  
  Purchase #5 $195.49   11.330%   $217.639   $217.64   $217.65   $217.60  
  Purchase #6 $95.77   6.533%   $102.0267   $102.03   $102.05   $102.00  
  Purchase #7 $208.64   13.197%   $236.1742   $236.17   $236.15   $236.20  
  7 purchase totals = $1,118.37       $1,248.2507   $1,248.25   $1,248.25   $1,248.10