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 $67.63   10.275%   $74.579   $74.58   $74.60   $74.60  
  Purchase #2 $245.75   10.788%   $272.2615   $272.26   $272.25   $272.30  
  Purchase #3 $77.77   9.440%   $85.1115   $85.11   $85.10   $85.10  
  Purchase #4 $61.89   4.632%   $64.7567   $64.76   $64.75   $64.80  
  Purchase #5 $16.30   4.449%   $17.0252   $17.03   $17.05   $17.00  
  Purchase #6 $98.32   3.392%   $101.655   $101.66   $101.65   $101.70  
  Purchase #7 $217.69   4.737%   $228.002   $228.00   $228.00   $228.00  
  7 purchase totals = $785.35       $843.3909   $843.40   $843.40   $843.50