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 $17.67   8.815%   $19.2276   $19.23   $19.25   $19.20  
  Purchase #2 $128.76   8.838%   $140.1398   $140.14   $140.15   $140.10  
  Purchase #3 $58.48   11.117%   $64.9812   $64.98   $65.00   $65.00  
  Purchase #4 $90.91   11.681%   $101.5292   $101.53   $101.55   $101.50  
  Purchase #5 $42.94   3.757%   $44.5533   $44.55   $44.55   $44.60  
  Purchase #6 $34.97   12.581%   $39.3696   $39.37   $39.35   $39.40  
  Purchase #7 $113.85   3.671%   $118.0294   $118.03   $118.05   $118.00  
  7 purchase totals = $487.58       $527.8301   $527.83   $527.90   $527.80