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 $191.41   11.819%   $214.0327   $214.03   $214.05   $214.00  
  Purchase #2 $58.75   3.551%   $60.8362   $60.84   $60.85   $60.80  
  Purchase #3 $190.66   10.366%   $210.4238   $210.42   $210.40   $210.40  
  Purchase #4 $139.91   11.231%   $155.6233   $155.62   $155.60   $155.60  
  Purchase #5 $203.63   6.536%   $216.9393   $216.94   $216.95   $216.90  
  Purchase #6 $224.78   7.331%   $241.2586   $241.26   $241.25   $241.30  
  Purchase #7 $167.81   11.539%   $187.1736   $187.17   $187.15   $187.20  
  7 purchase totals = $1,176.95       $1,286.2875   $1,286.28   $1,286.25   $1,286.20