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 $194.56   8.845%   $211.7688   $211.77   $211.75   $211.80  
  Purchase #2 $110.58   7.570%   $118.9509   $118.95   $118.95   $119.00  
  Purchase #3 $239.77   7.197%   $257.0262   $257.03   $257.05   $257.00  
  Purchase #4 $44.44   8.593%   $48.2587   $48.26   $48.25   $48.30  
  Purchase #5 $15.93   3.547%   $16.495   $16.50   $16.50   $16.50  
  Purchase #6 $11.75   4.285%   $12.2535   $12.25   $12.25   $12.30  
  Purchase #7 $210.49   10.711%   $233.0356   $233.04   $233.05   $233.00  
  7 purchase totals = $827.52       $897.7887   $897.80   $897.80   $897.90