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 $247.95   9.677%   $271.9441   $271.94   $271.95   $271.90  
  Purchase #2 $68.85   10.838%   $76.312   $76.31   $76.30   $76.30  
  Purchase #3 $203.79   7.693%   $219.4676   $219.47   $219.45   $219.50  
  Purchase #4 $186.29   7.643%   $200.5281   $200.53   $200.55   $200.50  
  Purchase #5 $161.61   3.449%   $167.1839   $167.18   $167.20   $167.20  
  Purchase #6 $224.94   12.623%   $253.3342   $253.33   $253.35   $253.30  
  Purchase #7 $42.46   9.813%   $46.6266   $46.63   $46.65   $46.60  
  7 purchase totals = $1,135.89       $1,235.3965   $1,235.39   $1,235.45   $1,235.30