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 $68.98   10.602%   $76.2933   $76.29   $76.30   $76.30  
  Purchase #2 $209.42   4.799%   $219.4701   $219.47   $219.45   $219.50  
  Purchase #3 $69.90   6.164%   $74.2086   $74.21   $74.20   $74.20  
  Purchase #4 $164.31   5.788%   $173.8203   $173.82   $173.80   $173.80  
  Purchase #5 $21.61   10.626%   $23.9063   $23.91   $23.90   $23.90  
  Purchase #6 $227.79   13.190%   $257.8355   $257.84   $257.85   $257.80  
  Purchase #7 $249.91   5.653%   $264.0374   $264.04   $264.05   $264.00  
  7 purchase totals = $1,011.92       $1,089.5715   $1,089.58   $1,089.55   $1,089.50