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 $62.46   11.315%   $69.5273   $69.53   $69.55   $69.50  
  Purchase #2 $90.92   11.297%   $101.1912   $101.19   $101.20   $101.20  
  Purchase #3 $248.73   7.330%   $266.9619   $266.96   $266.95   $267.00  
  Purchase #4 $74.69   7.194%   $80.0632   $80.06   $80.05   $80.10  
  Purchase #5 $146.25   8.468%   $158.6345   $158.63   $158.65   $158.60  
  Purchase #6 $84.54   8.114%   $91.3996   $91.40   $91.40   $91.40  
  Purchase #7 $163.54   9.503%   $179.0812   $179.08   $179.10   $179.10  
  7 purchase totals = $871.13       $946.8589   $946.85   $946.90   $946.90