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 $17.73   10.713%   $19.6294   $19.63   $19.65   $19.60  
  Purchase #2 $211.42   11.183%   $235.0631   $235.06   $235.05   $235.10  
  Purchase #3 $12.66   5.338%   $13.3358   $13.34   $13.35   $13.30  
  Purchase #4 $30.90   12.496%   $34.7613   $34.76   $34.75   $34.80  
  Purchase #5 $215.41   4.695%   $225.5235   $225.52   $225.50   $225.50  
  Purchase #6 $66.58   9.606%   $72.9757   $72.98   $73.00   $73.00  
  Purchase #7 $221.44   4.322%   $231.0106   $231.01   $231.00   $231.00  
  7 purchase totals = $776.14       $832.2994   $832.30   $832.30   $832.30