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 $166.61   11.524%   $185.8101   $185.81   $185.80   $185.80  
  Purchase #2 $89.43   13.853%   $101.8187   $101.82   $101.80   $101.80  
  Purchase #3 $15.49   4.385%   $16.1692   $16.17   $16.15   $16.20  
  Purchase #4 $106.59   13.834%   $121.3357   $121.34   $121.35   $121.30  
  Purchase #5 $239.69   9.744%   $263.0454   $263.05   $263.05   $263.00  
  Purchase #6 $32.42   5.317%   $34.1438   $34.14   $34.15   $34.10  
  Purchase #7 $61.93   13.844%   $70.5036   $70.50   $70.50   $70.50  
  7 purchase totals = $712.16       $792.8265   $792.83   $792.80   $792.70