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 $218.40   6.209%   $231.9605   $231.96   $231.95   $232.00  
  Purchase #2 $129.89   5.505%   $137.0404   $137.04   $137.05   $137.00  
  Purchase #3 $219.59   5.549%   $231.775   $231.78   $231.80   $231.80  
  Purchase #4 $152.61   11.337%   $169.9114   $169.91   $169.90   $169.90  
  Purchase #5 $216.52   8.513%   $234.9523   $234.95   $234.95   $235.00  
  Purchase #6 $225.94   3.797%   $234.5189   $234.52   $234.50   $234.50  
  Purchase #7 $98.82   4.259%   $103.0287   $103.03   $103.05   $103.00  
  7 purchase totals = $1,261.77       $1,343.1872   $1,343.19   $1,343.20   $1,343.20