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 $62.45   5.763%   $66.049   $66.05   $66.05   $66.00  
  Purchase #2 $32.43   11.113%   $36.0339   $36.03   $36.05   $36.00  
  Purchase #3 $160.70   5.724%   $169.8985   $169.90   $169.90   $169.90  
  Purchase #4 $109.68   12.776%   $123.6927   $123.69   $123.70   $123.70  
  Purchase #5 $192.52   10.652%   $213.0272   $213.03   $213.05   $213.00  
  Purchase #6 $216.60   3.193%   $223.516   $223.52   $223.50   $223.50  
  Purchase #7 $60.62   3.413%   $62.689   $62.69   $62.70   $62.70  
  7 purchase totals = $835.00       $894.9063   $894.91   $894.95   $894.80