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 $169.61   8.207%   $183.5299   $183.53   $183.55   $183.50  
  Purchase #2 $241.32   13.278%   $273.3625   $273.36   $273.35   $273.40  
  Purchase #3 $232.76   4.852%   $244.0535   $244.05   $244.05   $244.10  
  Purchase #4 $77.48   9.151%   $84.5702   $84.57   $84.55   $84.60  
  Purchase #5 $104.72   5.774%   $110.7665   $110.77   $110.75   $110.80  
  Purchase #6 $61.38   9.436%   $67.1718   $67.17   $67.15   $67.20  
  Purchase #7 $222.82   8.170%   $241.0244   $241.02   $241.00   $241.00  
  7 purchase totals = $1,110.09       $1,204.4788   $1,204.47   $1,204.40   $1,204.60