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 $61.77   8.121%   $66.7863   $66.79   $66.80   $66.80  
  Purchase #2 $119.67   10.339%   $132.0427   $132.04   $132.05   $132.00  
  Purchase #3 $43.49   5.834%   $46.0272   $46.03   $46.05   $46.00  
  Purchase #4 $224.79   13.280%   $254.6421   $254.64   $254.65   $254.60  
  Purchase #5 $218.32   6.292%   $232.0567   $232.06   $232.05   $232.10  
  Purchase #6 $5.95   3.417%   $6.1533   $6.15   $6.15   $6.20  
  Purchase #7 $112.25   6.673%   $119.7404   $119.74   $119.75   $119.70  
  7 purchase totals = $786.24       $857.4487   $857.45   $857.50   $857.40