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 $55.87   8.280%   $60.496   $60.50   $60.50   $60.50  
  Purchase #2 $38.37   13.631%   $43.6002   $43.60   $43.60   $43.60  
  Purchase #3 $56.79   7.832%   $61.2378   $61.24   $61.25   $61.20  
  Purchase #4 $70.79   3.498%   $73.2662   $73.27   $73.25   $73.30  
  Purchase #5 $55.84   8.865%   $60.7902   $60.79   $60.80   $60.80  
  Purchase #6 $26.76   12.341%   $30.0625   $30.06   $30.05   $30.10  
  Purchase #7 $163.29   13.144%   $184.7528   $184.75   $184.75   $184.80  
  7 purchase totals = $467.71       $514.2057   $514.21   $514.20   $514.30