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 $206.71   13.338%   $234.281   $234.28   $234.30   $234.30  
  Purchase #2 $140.42   11.501%   $156.5697   $156.57   $156.55   $156.60  
  Purchase #3 $20.82   10.623%   $23.0317   $23.03   $23.05   $23.00  
  Purchase #4 $206.56   5.659%   $218.2492   $218.25   $218.25   $218.20  
  Purchase #5 $184.88   11.560%   $206.2521   $206.25   $206.25   $206.30  
  Purchase #6 $159.89   11.797%   $178.7522   $178.75   $178.75   $178.80  
  Purchase #7 $205.31   5.574%   $216.754   $216.75   $216.75   $216.80  
  7 purchase totals = $1,124.59       $1,233.8899   $1,233.88   $1,233.90   $1,234.00