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 $33.68   6.167%   $35.757   $35.76   $35.75   $35.80  
  Purchase #2 $175.73   4.366%   $183.4024   $183.40   $183.40   $183.40  
  Purchase #3 $225.92   3.112%   $232.9506   $232.95   $232.95   $233.00  
  Purchase #4 $60.34   7.792%   $65.0417   $65.04   $65.05   $65.00  
  Purchase #5 $40.35   9.280%   $44.0945   $44.09   $44.10   $44.10  
  Purchase #6 $175.39   3.852%   $182.146   $182.15   $182.15   $182.10  
  Purchase #7 $69.46   8.716%   $75.5141   $75.51   $75.50   $75.50  
  7 purchase totals = $780.87       $818.9063   $818.90   $818.90   $818.90