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 $60.97   11.722%   $68.1169   $68.12   $68.10   $68.10  
  Purchase #2 $60.36   9.181%   $65.9017   $65.90   $65.90   $65.90  
  Purchase #3 $101.33   5.584%   $106.9883   $106.99   $107.00   $107.00  
  Purchase #4 $64.48   13.743%   $73.3415   $73.34   $73.35   $73.30  
  Purchase #5 $72.87   3.756%   $75.607   $75.61   $75.60   $75.60  
  Purchase #6 $64.31   11.652%   $71.8034   $71.80   $71.80   $71.80  
  Purchase #7 $12.63   12.230%   $14.1746   $14.17   $14.15   $14.20  
  7 purchase totals = $436.95       $475.9334   $475.93   $475.90   $475.90