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 $142.52   4.566%   $149.0275   $149.03   $149.05   $149.00  
  Purchase #2 $216.70   9.193%   $236.6212   $236.62   $236.60   $236.60  
  Purchase #3 $157.27   13.123%   $177.9085   $177.91   $177.90   $177.90  
  Purchase #4 $113.69   3.661%   $117.8522   $117.85   $117.85   $117.90  
  Purchase #5 $72.33   10.242%   $79.738   $79.74   $79.75   $79.70  
  Purchase #6 $99.28   11.429%   $110.6267   $110.63   $110.65   $110.60  
  Purchase #7 $166.43   13.533%   $188.953   $188.95   $188.95   $189.00  
  7 purchase totals = $968.22       $1,060.7271   $1,060.73   $1,060.75   $1,060.70