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 $68.86   12.183%   $77.2492   $77.25   $77.25   $77.20  
  Purchase #2 $141.30   5.706%   $149.3626   $149.36   $149.35   $149.40  
  Purchase #3 $15.39   9.206%   $16.8068   $16.81   $16.80   $16.80  
  Purchase #4 $172.27   6.700%   $183.8121   $183.81   $183.80   $183.80  
  Purchase #5 $145.87   4.338%   $152.1978   $152.20   $152.20   $152.20  
  Purchase #6 $216.48   13.556%   $245.826   $245.83   $245.85   $245.80  
  Purchase #7 $227.58   7.283%   $244.1547   $244.15   $244.15   $244.20  
  7 purchase totals = $987.75       $1,069.4092   $1,069.41   $1,069.40   $1,069.40