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 $62.27   13.182%   $70.4784   $70.48   $70.50   $70.50  
  Purchase #2 $14.47   10.714%   $16.0203   $16.02   $16.00   $16.00  
  Purchase #3 $48.91   13.312%   $55.4209   $55.42   $55.40   $55.40  
  Purchase #4 $87.59   6.684%   $93.4445   $93.44   $93.45   $93.40  
  Purchase #5 $166.71   5.734%   $176.2692   $176.27   $176.25   $176.30  
  Purchase #6 $27.33   4.744%   $28.6265   $28.63   $28.65   $28.60  
  Purchase #7 $23.89   13.385%   $27.0877   $27.09   $27.10   $27.10  
  7 purchase totals = $431.17       $467.3475   $467.35   $467.35   $467.30