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 $32.95   5.719%   $34.8344   $34.83   $34.85   $34.80  
  Purchase #2 $40.65   10.271%   $44.8252   $44.83   $44.85   $44.80  
  Purchase #3 $57.33   11.429%   $63.8822   $63.88   $63.90   $63.90  
  Purchase #4 $52.39   7.397%   $56.2653   $56.27   $56.25   $56.30  
  Purchase #5 $174.50   5.607%   $184.2842   $184.28   $184.30   $184.30  
  Purchase #6 $200.95   5.240%   $211.4798   $211.48   $211.50   $211.50  
  Purchase #7 $140.58   3.124%   $144.9717   $144.97   $144.95   $145.00  
  7 purchase totals = $699.35       $740.5428   $740.54   $740.60   $740.60