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 $55.26   5.793%   $58.4612   $58.46   $58.45   $58.50  
  Purchase #2 $60.71   3.490%   $62.8288   $62.83   $62.85   $62.80  
  Purchase #3 $194.56   13.501%   $220.8275   $220.83   $220.85   $220.80  
  Purchase #4 $40.98   13.775%   $46.625   $46.63   $46.65   $46.60  
  Purchase #5 $226.26   11.847%   $253.065   $253.07   $253.05   $253.10  
  Purchase #6 $198.56   12.544%   $223.4674   $223.47   $223.45   $223.50  
  Purchase #7 $65.84   9.124%   $71.8472   $71.85   $71.85   $71.80  
  7 purchase totals = $842.17       $937.1221   $937.14   $937.15   $937.10