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 $208.52   8.501%   $226.2463   $226.25   $226.25   $226.20  
  Purchase #2 $224.91   5.136%   $236.4614   $236.46   $236.45   $236.50  
  Purchase #3 $154.36   7.364%   $165.7271   $165.73   $165.75   $165.70  
  Purchase #4 $6.26   4.316%   $6.5302   $6.53   $6.55   $6.50  
  Purchase #5 $99.81   13.145%   $112.93   $112.93   $112.95   $112.90  
  Purchase #6 $121.82   9.469%   $133.3551   $133.36   $133.35   $133.40  
  Purchase #7 $80.82   5.700%   $85.4267   $85.43   $85.45   $85.40  
  7 purchase totals = $896.50       $966.6768   $966.69   $966.75   $966.60