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 $62.63   8.739%   $68.1032   $68.10   $68.10   $68.10  
  Purchase #2 $224.35   11.116%   $249.2887   $249.29   $249.30   $249.30  
  Purchase #3 $230.83   6.347%   $245.4808   $245.48   $245.50   $245.50  
  Purchase #4 $70.34   7.292%   $75.4692   $75.47   $75.45   $75.50  
  Purchase #5 $222.25   13.216%   $251.6226   $251.62   $251.60   $251.60  
  Purchase #6 $32.66   13.322%   $37.011   $37.01   $37.00   $37.00  
  Purchase #7 $188.36   12.854%   $212.5718   $212.57   $212.55   $212.60  
  7 purchase totals = $1,031.42       $1,139.5473   $1,139.54   $1,139.50   $1,139.60