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 $62.27   7.819%   $67.1389   $67.14   $67.15   $67.10  
  Purchase #2 $194.62   11.393%   $216.7931   $216.79   $216.80   $216.80  
  Purchase #3 $50.87   3.570%   $52.6861   $52.69   $52.70   $52.70  
  Purchase #4 $78.94   13.313%   $89.4493   $89.45   $89.45   $89.40  
  Purchase #5 $195.45   3.251%   $201.8041   $201.80   $201.80   $201.80  
  Purchase #6 $124.39   5.371%   $131.071   $131.07   $131.05   $131.10  
  Purchase #7 $242.83   3.199%   $250.5981   $250.60   $250.60   $250.60  
  7 purchase totals = $949.37       $1,009.5406   $1,009.54   $1,009.55   $1,009.50