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 $67.94   9.450%   $74.3603   $74.36   $74.35   $74.40  
  Purchase #2 $243.31   9.687%   $266.8794   $266.88   $266.90   $266.90  
  Purchase #3 $5.66   9.376%   $6.1907   $6.19   $6.20   $6.20  
  Purchase #4 $90.83   6.244%   $96.5014   $96.50   $96.50   $96.50  
  Purchase #5 $220.56   8.486%   $239.2767   $239.28   $239.30   $239.30  
  Purchase #6 $166.92   5.534%   $176.1574   $176.16   $176.15   $176.20  
  Purchase #7 $60.51   11.292%   $67.3428   $67.34   $67.35   $67.30  
  7 purchase totals = $855.73       $926.7087   $926.71   $926.75   $926.80