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 $41.77   8.214%   $45.201   $45.20   $45.20   $45.20  
  Purchase #2 $13.79   10.601%   $15.2519   $15.25   $15.25   $15.30  
  Purchase #3 $204.51   8.587%   $222.0713   $222.07   $222.05   $222.10  
  Purchase #4 $42.58   5.198%   $44.7933   $44.79   $44.80   $44.80  
  Purchase #5 $166.57   3.502%   $172.4033   $172.40   $172.40   $172.40  
  Purchase #6 $218.42   11.700%   $243.9751   $243.98   $244.00   $244.00  
  Purchase #7 $45.81   9.582%   $50.1995   $50.20   $50.20   $50.20  
  7 purchase totals = $733.45       $793.8954   $793.89   $793.90   $794.00