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 $92.69   5.635%   $97.9131   $97.91   $97.90   $97.90  
  Purchase #2 $67.52   8.493%   $73.2545   $73.25   $73.25   $73.30  
  Purchase #3 $164.64   11.545%   $183.6477   $183.65   $183.65   $183.60  
  Purchase #4 $94.96   8.147%   $102.6964   $102.70   $102.70   $102.70  
  Purchase #5 $61.93   13.682%   $70.4033   $70.40   $70.40   $70.40  
  Purchase #6 $239.69   3.394%   $247.8251   $247.83   $247.85   $247.80  
  Purchase #7 $216.65   13.585%   $246.0819   $246.08   $246.10   $246.10  
  7 purchase totals = $938.08       $1,021.8220   $1,021.82   $1,021.85   $1,021.80