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 $209.26   8.171%   $226.3586   $226.36   $226.35   $226.40  
  Purchase #2 $40.96   5.724%   $43.3046   $43.30   $43.30   $43.30  
  Purchase #3 $170.73   5.216%   $179.6353   $179.64   $179.65   $179.60  
  Purchase #4 $116.95   8.556%   $126.9562   $126.96   $126.95   $127.00  
  Purchase #5 $169.52   8.400%   $183.7597   $183.76   $183.75   $183.80  
  Purchase #6 $61.46   6.585%   $65.5071   $65.51   $65.50   $65.50  
  Purchase #7 $61.64   13.163%   $69.7537   $69.75   $69.75   $69.80  
  7 purchase totals = $830.52       $895.2752   $895.28   $895.25   $895.40