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 $64.34   9.617%   $70.5276   $70.53   $70.55   $70.50  
  Purchase #2 $245.55   4.764%   $257.248   $257.25   $257.25   $257.20  
  Purchase #3 $64.30   6.226%   $68.3033   $68.30   $68.30   $68.30  
  Purchase #4 $195.34   6.810%   $208.6427   $208.64   $208.65   $208.60  
  Purchase #5 $191.75   12.869%   $216.4263   $216.43   $216.45   $216.40  
  Purchase #6 $240.67   5.118%   $252.9875   $252.99   $253.00   $253.00  
  Purchase #7 $191.54   11.865%   $214.2662   $214.27   $214.25   $214.30  
  7 purchase totals = $1,193.49       $1,288.4016   $1,288.41   $1,288.45   $1,288.30