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 $219.94   12.227%   $246.8321   $246.83   $246.85   $246.80  
  Purchase #2 $223.99   11.375%   $249.4689   $249.47   $249.45   $249.50  
  Purchase #3 $71.57   4.198%   $74.5745   $74.57   $74.55   $74.60  
  Purchase #4 $84.44   4.276%   $88.0507   $88.05   $88.05   $88.10  
  Purchase #5 $188.37   3.405%   $194.784   $194.78   $194.80   $194.80  
  Purchase #6 $51.88   4.358%   $54.1409   $54.14   $54.15   $54.10  
  Purchase #7 $67.93   8.379%   $73.6219   $73.62   $73.60   $73.60  
  7 purchase totals = $908.12       $981.4730   $981.46   $981.45   $981.50