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 $57.95   6.786%   $61.8825   $61.88   $61.90   $61.90  
  Purchase #2 $225.68   8.117%   $243.9984   $244.00   $244.00   $244.00  
  Purchase #3 $41.28   8.525%   $44.7991   $44.80   $44.80   $44.80  
  Purchase #4 $95.34   12.136%   $106.9105   $106.91   $106.90   $106.90  
  Purchase #5 $99.65   9.451%   $109.0679   $109.07   $109.05   $109.10  
  Purchase #6 $192.30   13.168%   $217.6221   $217.62   $217.60   $217.60  
  Purchase #7 $32.44   3.259%   $33.4972   $33.50   $33.50   $33.50  
  7 purchase totals = $744.64       $817.7777   $817.78   $817.75   $817.80