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 $61.71   4.560%   $64.524   $64.52   $64.50   $64.50  
  Purchase #2 $92.71   10.755%   $102.681   $102.68   $102.70   $102.70  
  Purchase #3 $90.48   11.214%   $100.6264   $100.63   $100.65   $100.60  
  Purchase #4 $233.64   11.623%   $260.796   $260.80   $260.80   $260.80  
  Purchase #5 $92.82   6.566%   $98.9146   $98.91   $98.90   $98.90  
  Purchase #6 $243.82   13.155%   $275.8945   $275.89   $275.90   $275.90  
  Purchase #7 $24.99   7.624%   $26.8952   $26.90   $26.90   $26.90  
  7 purchase totals = $840.17       $930.3317   $930.33   $930.35   $930.30