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 $58.62   5.653%   $61.9338   $61.93   $61.95   $61.90  
  Purchase #2 $210.48   4.436%   $219.8169   $219.82   $219.80   $219.80  
  Purchase #3 $98.40   12.307%   $110.5101   $110.51   $110.50   $110.50  
  Purchase #4 $78.41   3.397%   $81.0736   $81.07   $81.05   $81.10  
  Purchase #5 $14.99   9.525%   $16.4178   $16.42   $16.40   $16.40  
  Purchase #6 $189.42   5.498%   $199.8343   $199.83   $199.85   $199.80  
  Purchase #7 $61.93   12.819%   $69.8688   $69.87   $69.85   $69.90  
  7 purchase totals = $712.25       $759.4553   $759.45   $759.40   $759.40