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 $56.78   3.622%   $58.8366   $58.84   $58.85   $58.80  
  Purchase #2 $32.55   9.502%   $35.6429   $35.64   $35.65   $35.60  
  Purchase #3 $140.63   11.543%   $156.8629   $156.86   $156.85   $156.90  
  Purchase #4 $250.25   5.359%   $263.6609   $263.66   $263.65   $263.70  
  Purchase #5 $75.33   7.120%   $80.6935   $80.69   $80.70   $80.70  
  Purchase #6 $60.50   11.673%   $67.5622   $67.56   $67.55   $67.60  
  Purchase #7 $96.29   8.293%   $104.2753   $104.28   $104.30   $104.30  
  7 purchase totals = $712.33       $767.5343   $767.53   $767.55   $767.60