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 $243.70   4.556%   $254.803   $254.80   $254.80   $254.80  
  Purchase #2 $91.35   4.233%   $95.2168   $95.22   $95.20   $95.20  
  Purchase #3 $118.43   7.848%   $127.7244   $127.72   $127.70   $127.70  
  Purchase #4 $250.48   6.255%   $266.1475   $266.15   $266.15   $266.10  
  Purchase #5 $57.84   3.446%   $59.8332   $59.83   $59.85   $59.80  
  Purchase #6 $42.39   5.277%   $44.6269   $44.63   $44.65   $44.60  
  Purchase #7 $14.38   3.860%   $14.9351   $14.94   $14.95   $14.90  
  7 purchase totals = $818.57       $863.2869   $863.29   $863.30   $863.10