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 $53.58   12.577%   $60.3188   $60.32   $60.30   $60.30  
  Purchase #2 $156.28   4.678%   $163.5908   $163.59   $163.60   $163.60  
  Purchase #3 $249.42   9.869%   $274.0353   $274.04   $274.05   $274.00  
  Purchase #4 $69.67   11.362%   $77.5859   $77.59   $77.60   $77.60  
  Purchase #5 $52.95   6.799%   $56.5501   $56.55   $56.55   $56.60  
  Purchase #6 $103.41   7.723%   $111.3964   $111.40   $111.40   $111.40  
  Purchase #7 $62.74   9.517%   $68.711   $68.71   $68.70   $68.70  
  7 purchase totals = $748.05       $812.1883   $812.20   $812.20   $812.20