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 $105.52   13.827%   $120.1103   $120.11   $120.10   $120.10  
  Purchase #2 $141.56   11.371%   $157.6568   $157.66   $157.65   $157.70  
  Purchase #3 $23.91   9.817%   $26.2572   $26.26   $26.25   $26.30  
  Purchase #4 $119.25   3.697%   $123.6587   $123.66   $123.65   $123.70  
  Purchase #5 $243.82   8.222%   $263.8669   $263.87   $263.85   $263.90  
  Purchase #6 $90.85   6.773%   $97.0033   $97.00   $97.00   $97.00  
  Purchase #7 $216.90   8.826%   $236.0436   $236.04   $236.05   $236.00  
  7 purchase totals = $941.81       $1,024.5968   $1,024.60   $1,024.55   $1,024.70