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 $174.81   13.415%   $198.2608   $198.26   $198.25   $198.30  
  Purchase #2 $245.47   9.548%   $268.9075   $268.91   $268.90   $268.90  
  Purchase #3 $19.81   5.782%   $20.9554   $20.96   $20.95   $21.00  
  Purchase #4 $205.69   3.643%   $213.1833   $213.18   $213.20   $213.20  
  Purchase #5 $49.97   9.322%   $54.6282   $54.63   $54.65   $54.60  
  Purchase #6 $38.92   13.663%   $44.2376   $44.24   $44.25   $44.20  
  Purchase #7 $249.30   5.313%   $262.5453   $262.55   $262.55   $262.50  
  7 purchase totals = $983.97       $1,062.7181   $1,062.73   $1,062.75   $1,062.70