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 $203.38   7.533%   $218.7006   $218.70   $218.70   $218.70  
  Purchase #2 $178.47   7.680%   $192.1765   $192.18   $192.20   $192.20  
  Purchase #3 $212.88   5.234%   $224.0221   $224.02   $224.00   $224.00  
  Purchase #4 $216.43   11.260%   $240.8   $240.80   $240.80   $240.80  
  Purchase #5 $227.61   6.601%   $242.6345   $242.63   $242.65   $242.60  
  Purchase #6 $54.66   7.417%   $58.7141   $58.71   $58.70   $58.70  
  Purchase #7 $91.49   5.574%   $96.5897   $96.59   $96.60   $96.60  
  7 purchase totals = $1,184.92       $1,273.6375   $1,273.63   $1,273.65   $1,273.60