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 $54.94   7.839%   $59.2467   $59.25   $59.25   $59.20  
  Purchase #2 $192.63   12.623%   $216.9457   $216.95   $216.95   $216.90  
  Purchase #3 $118.33   12.685%   $133.3402   $133.34   $133.35   $133.30  
  Purchase #4 $241.35   6.197%   $256.3065   $256.31   $256.30   $256.30  
  Purchase #5 $121.55   12.853%   $137.1728   $137.17   $137.15   $137.20  
  Purchase #6 $178.52   13.172%   $202.0347   $202.03   $202.05   $202.00  
  Purchase #7 $17.34   5.586%   $18.3086   $18.31   $18.30   $18.30  
  7 purchase totals = $924.66       $1,023.3552   $1,023.36   $1,023.35   $1,023.20