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 $60.72   13.616%   $68.9876   $68.99   $69.00   $69.00  
  Purchase #2 $225.34   13.376%   $255.4815   $255.48   $255.50   $255.50  
  Purchase #3 $150.60   10.784%   $166.8407   $166.84   $166.85   $166.80  
  Purchase #4 $25.86   10.766%   $28.6441   $28.64   $28.65   $28.60  
  Purchase #5 $59.89   11.758%   $66.9319   $66.93   $66.95   $66.90  
  Purchase #6 $203.46   4.147%   $211.8975   $211.90   $211.90   $211.90  
  Purchase #7 $21.99   8.722%   $23.908   $23.91   $23.90   $23.90  
  7 purchase totals = $747.86       $822.6913   $822.69   $822.75   $822.60