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 $86.64   9.256%   $94.6594   $94.66   $94.65   $94.70  
  Purchase #2 $58.52   3.712%   $60.6923   $60.69   $60.70   $60.70  
  Purchase #3 $235.91   9.227%   $257.6774   $257.68   $257.70   $257.70  
  Purchase #4 $144.92   11.361%   $161.3844   $161.38   $161.40   $161.40  
  Purchase #5 $25.32   7.261%   $27.1585   $27.16   $27.15   $27.20  
  Purchase #6 $11.80   8.797%   $12.838   $12.84   $12.85   $12.80  
  Purchase #7 $10.64   3.697%   $11.0334   $11.03   $11.05   $11.00  
  7 purchase totals = $573.75       $625.4434   $625.44   $625.50   $625.50