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 $171.66   12.784%   $193.605   $193.61   $193.60   $193.60  
  Purchase #2 $119.66   4.789%   $125.3905   $125.39   $125.40   $125.40  
  Purchase #3 $139.79   6.339%   $148.6513   $148.65   $148.65   $148.70  
  Purchase #4 $18.86   10.656%   $20.8697   $20.87   $20.85   $20.90  
  Purchase #5 $213.64   10.362%   $235.7774   $235.78   $235.80   $235.80  
  Purchase #6 $230.59   5.847%   $244.0726   $244.07   $244.05   $244.10  
  Purchase #7 $52.64   3.431%   $54.4461   $54.45   $54.45   $54.40  
  7 purchase totals = $946.84       $1,022.8126   $1,022.82   $1,022.80   $1,022.90