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 $247.27   8.726%   $268.8468   $268.85   $268.85   $268.80  
  Purchase #2 $51.66   6.271%   $54.8996   $54.90   $54.90   $54.90  
  Purchase #3 $235.44   6.490%   $250.7201   $250.72   $250.70   $250.70  
  Purchase #4 $110.25   9.520%   $120.7458   $120.75   $120.75   $120.70  
  Purchase #5 $218.57   9.484%   $239.2992   $239.30   $239.30   $239.30  
  Purchase #6 $63.51   4.473%   $66.3508   $66.35   $66.35   $66.40  
  Purchase #7 $226.41   6.671%   $241.5138   $241.51   $241.50   $241.50  
  7 purchase totals = $1,153.11       $1,242.3761   $1,242.38   $1,242.35   $1,242.30