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 $193.91   5.366%   $204.3152   $204.32   $204.30   $204.30  
  Purchase #2 $166.42   5.141%   $174.9757   $174.98   $175.00   $175.00  
  Purchase #3 $73.66   4.866%   $77.2443   $77.24   $77.25   $77.20  
  Purchase #4 $184.90   4.394%   $193.0245   $193.02   $193.00   $193.00  
  Purchase #5 $112.90   12.424%   $126.9267   $126.93   $126.95   $126.90  
  Purchase #6 $117.28   12.554%   $132.0033   $132.00   $132.00   $132.00  
  Purchase #7 $89.28   4.316%   $93.1333   $93.13   $93.15   $93.10  
  7 purchase totals = $938.35       $1,001.6230   $1,001.62   $1,001.65   $1,001.50