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 $223.42   12.451%   $251.238   $251.24   $251.25   $251.20  
  Purchase #2 $218.66   12.433%   $245.846   $245.85   $245.85   $245.80  
  Purchase #3 $178.64   10.701%   $197.7563   $197.76   $197.75   $197.80  
  Purchase #4 $22.67   8.482%   $24.5929   $24.59   $24.60   $24.60  
  Purchase #5 $216.95   9.141%   $236.7814   $236.78   $236.80   $236.80  
  Purchase #6 $226.27   7.590%   $243.4439   $243.44   $243.45   $243.40  
  Purchase #7 $242.38   9.698%   $265.886   $265.89   $265.90   $265.90  
  7 purchase totals = $1,328.99       $1,465.5445   $1,465.55   $1,465.60   $1,465.50