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 $61.42   13.777%   $69.8818   $69.88   $69.90   $69.90  
  Purchase #2 $162.41   12.175%   $182.1834   $182.18   $182.20   $182.20  
  Purchase #3 $62.67   8.779%   $68.1718   $68.17   $68.15   $68.20  
  Purchase #4 $87.49   9.744%   $96.015   $96.02   $96.00   $96.00  
  Purchase #5 $121.88   12.837%   $137.5257   $137.53   $137.55   $137.50  
  Purchase #6 $170.31   3.483%   $176.2419   $176.24   $176.25   $176.20  
  Purchase #7 $171.90   13.602%   $195.2818   $195.28   $195.30   $195.30  
  7 purchase totals = $838.08       $925.3014   $925.30   $925.35   $925.30