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 $24.37   6.541%   $25.964   $25.96   $25.95   $26.00  
  Purchase #2 $49.43   6.565%   $52.6751   $52.68   $52.70   $52.70  
  Purchase #3 $169.34   10.388%   $186.931   $186.93   $186.95   $186.90  
  Purchase #4 $217.79   8.827%   $237.0143   $237.01   $237.00   $237.00  
  Purchase #5 $45.64   6.307%   $48.5185   $48.52   $48.50   $48.50  
  Purchase #6 $246.69   11.581%   $275.2592   $275.26   $275.25   $275.30  
  Purchase #7 $71.99   10.388%   $79.4683   $79.47   $79.45   $79.50  
  7 purchase totals = $825.25       $905.8304   $905.83   $905.80   $905.90