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 $59.37   4.138%   $61.8267   $61.83   $61.85   $61.80  
  Purchase #2 $47.90   8.442%   $51.9437   $51.94   $51.95   $51.90  
  Purchase #3 $134.36   6.327%   $142.861   $142.86   $142.85   $142.90  
  Purchase #4 $220.44   5.175%   $231.8478   $231.85   $231.85   $231.80  
  Purchase #5 $60.92   13.599%   $69.2045   $69.20   $69.20   $69.20  
  Purchase #6 $206.31   13.587%   $234.3413   $234.34   $234.35   $234.30  
  Purchase #7 $229.68   10.616%   $254.0628   $254.06   $254.05   $254.10  
  7 purchase totals = $958.98       $1,046.0878   $1,046.08   $1,046.10   $1,046.00