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 $92.99   3.314%   $96.0717   $96.07   $96.05   $96.10  
  Purchase #2 $142.44   4.325%   $148.6005   $148.60   $148.60   $148.60  
  Purchase #3 $13.93   9.778%   $15.2921   $15.29   $15.30   $15.30  
  Purchase #4 $223.32   5.493%   $235.587   $235.59   $235.60   $235.60  
  Purchase #5 $49.66   13.582%   $56.4048   $56.40   $56.40   $56.40  
  Purchase #6 $232.97   4.197%   $242.7478   $242.75   $242.75   $242.70  
  Purchase #7 $54.31   8.627%   $58.9953   $59.00   $59.00   $59.00  
  7 purchase totals = $809.62       $853.6992   $853.70   $853.70   $853.70