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 $69.36   8.196%   $75.0447   $75.04   $75.05   $75.00  
  Purchase #2 $238.59   12.776%   $269.0723   $269.07   $269.05   $269.10  
  Purchase #3 $11.71   10.591%   $12.9502   $12.95   $12.95   $13.00  
  Purchase #4 $224.79   13.505%   $255.1479   $255.15   $255.15   $255.10  
  Purchase #5 $27.99   5.666%   $29.5759   $29.58   $29.60   $29.60  
  Purchase #6 $107.64   9.319%   $117.671   $117.67   $117.65   $117.70  
  Purchase #7 $78.56   6.434%   $83.6146   $83.61   $83.60   $83.60  
  7 purchase totals = $758.64       $843.0766   $843.07   $843.05   $843.10