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 $70.82   8.641%   $76.9396   $76.94   $76.95   $76.90  
  Purchase #2 $235.96   8.478%   $255.9647   $255.96   $255.95   $256.00  
  Purchase #3 $73.33   8.197%   $79.3409   $79.34   $79.35   $79.30  
  Purchase #4 $190.34   10.746%   $210.7939   $210.79   $210.80   $210.80  
  Purchase #5 $125.45   13.766%   $142.7194   $142.72   $142.70   $142.70  
  Purchase #6 $16.27   12.716%   $18.3389   $18.34   $18.35   $18.30  
  Purchase #7 $241.56   4.681%   $252.8674   $252.87   $252.85   $252.90  
  7 purchase totals = $953.73       $1,036.9648   $1,036.96   $1,036.95   $1,036.90