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 $56.41   9.731%   $61.8993   $61.90   $61.90   $61.90  
  Purchase #2 $245.37   3.621%   $254.2548   $254.25   $254.25   $254.30  
  Purchase #3 $47.89   10.222%   $52.7853   $52.79   $52.80   $52.80  
  Purchase #4 $40.92   9.335%   $44.7399   $44.74   $44.75   $44.70  
  Purchase #5 $84.45   7.587%   $90.8572   $90.86   $90.85   $90.90  
  Purchase #6 $250.26   10.541%   $276.6399   $276.64   $276.65   $276.60  
  Purchase #7 $216.88   3.731%   $224.9718   $224.97   $224.95   $225.00  
  7 purchase totals = $942.18       $1,006.1482   $1,006.15   $1,006.15   $1,006.20