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 $55.56   6.604%   $59.2292   $59.23   $59.25   $59.20  
  Purchase #2 $202.51   5.297%   $213.237   $213.24   $213.25   $213.20  
  Purchase #3 $195.59   4.423%   $204.2409   $204.24   $204.25   $204.20  
  Purchase #4 $181.50   3.513%   $187.8761   $187.88   $187.90   $187.90  
  Purchase #5 $44.43   7.566%   $47.7916   $47.79   $47.80   $47.80  
  Purchase #6 $236.54   12.259%   $265.5374   $265.54   $265.55   $265.50  
  Purchase #7 $40.90   9.430%   $44.7569   $44.76   $44.75   $44.80  
  7 purchase totals = $957.03       $1,022.6691   $1,022.68   $1,022.75   $1,022.60