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 $68.81   4.103%   $71.6333   $71.63   $71.65   $71.60  
  Purchase #2 $9.99   13.276%   $11.3163   $11.32   $11.30   $11.30  
  Purchase #3 $199.47   12.373%   $224.1504   $224.15   $224.15   $224.20  
  Purchase #4 $135.49   10.355%   $149.52   $149.52   $149.50   $149.50  
  Purchase #5 $206.79   9.406%   $226.2407   $226.24   $226.25   $226.20  
  Purchase #6 $169.65   9.281%   $185.3952   $185.40   $185.40   $185.40  
  Purchase #7 $25.63   8.529%   $27.816   $27.82   $27.80   $27.80  
  7 purchase totals = $815.83       $896.0719   $896.08   $896.05   $896.00