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 $91.80   4.817%   $96.222   $96.22   $96.20   $96.20  
  Purchase #2 $126.41   7.112%   $135.4003   $135.40   $135.40   $135.40  
  Purchase #3 $39.26   3.440%   $40.6105   $40.61   $40.60   $40.60  
  Purchase #4 $244.36   8.798%   $265.8588   $265.86   $265.85   $265.90  
  Purchase #5 $71.93   5.772%   $76.0818   $76.08   $76.10   $76.10  
  Purchase #6 $96.28   11.106%   $106.9729   $106.97   $106.95   $107.00  
  Purchase #7 $207.44   9.867%   $227.9081   $227.91   $227.90   $227.90  
  7 purchase totals = $877.48       $949.0544   $949.05   $949.00   $949.10