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 $68.61   7.196%   $73.5472   $73.55   $73.55   $73.50  
  Purchase #2 $115.29   3.811%   $119.6837   $119.68   $119.70   $119.70  
  Purchase #3 $213.29   13.369%   $241.8047   $241.80   $241.80   $241.80  
  Purchase #4 $107.54   8.734%   $116.9325   $116.93   $116.95   $116.90  
  Purchase #5 $113.60   11.651%   $126.8355   $126.84   $126.85   $126.80  
  Purchase #6 $5.40   10.797%   $5.983   $5.98   $6.00   $6.00  
  Purchase #7 $66.74   11.114%   $74.1575   $74.16   $74.15   $74.20  
  7 purchase totals = $690.47       $758.9441   $758.94   $759.00   $758.90