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 $105.30   7.644%   $113.3491   $113.35   $113.35   $113.30  
  Purchase #2 $169.79   8.784%   $184.7044   $184.70   $184.70   $184.70  
  Purchase #3 $175.52   12.595%   $197.6267   $197.63   $197.65   $197.60  
  Purchase #4 $44.96   13.247%   $50.9159   $50.92   $50.90   $50.90  
  Purchase #5 $88.74   5.610%   $93.7183   $93.72   $93.70   $93.70  
  Purchase #6 $208.59   3.468%   $215.8239   $215.82   $215.80   $215.80  
  Purchase #7 $231.89   12.553%   $260.9992   $261.00   $261.00   $261.00  
  7 purchase totals = $1,024.79       $1,117.1375   $1,117.14   $1,117.10   $1,117.00