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 $248.65   9.144%   $271.3866   $271.39   $271.40   $271.40  
  Purchase #2 $9.27   9.565%   $10.1567   $10.16   $10.15   $10.20  
  Purchase #3 $210.34   5.412%   $221.7236   $221.72   $221.70   $221.70  
  Purchase #4 $44.89   3.391%   $46.4122   $46.41   $46.40   $46.40  
  Purchase #5 $213.66   5.573%   $225.5673   $225.57   $225.55   $225.60  
  Purchase #6 $204.25   13.722%   $232.2772   $232.28   $232.30   $232.30  
  Purchase #7 $47.87   11.546%   $53.3971   $53.40   $53.40   $53.40  
  7 purchase totals = $978.93       $1,060.9207   $1,060.93   $1,060.90   $1,061.00