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 $23.59   12.414%   $26.5185   $26.52   $26.50   $26.50  
  Purchase #2 $220.95   3.789%   $229.3218   $229.32   $229.30   $229.30  
  Purchase #3 $97.86   10.485%   $108.1206   $108.12   $108.10   $108.10  
  Purchase #4 $5.30   3.137%   $5.4663   $5.47   $5.45   $5.50  
  Purchase #5 $177.99   4.858%   $186.6368   $186.64   $186.65   $186.60  
  Purchase #6 $120.94   9.139%   $131.9927   $131.99   $132.00   $132.00  
  Purchase #7 $205.88   7.292%   $220.8928   $220.89   $220.90   $220.90  
  7 purchase totals = $852.51       $908.9495   $908.95   $908.90   $908.90