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 $62.26   5.344%   $65.5872   $65.59   $65.60   $65.60  
  Purchase #2 $141.62   6.659%   $151.0505   $151.05   $151.05   $151.10  
  Purchase #3 $246.42   8.235%   $266.7127   $266.71   $266.70   $266.70  
  Purchase #4 $173.67   11.364%   $193.4059   $193.41   $193.40   $193.40  
  Purchase #5 $45.82   4.509%   $47.886   $47.89   $47.90   $47.90  
  Purchase #6 $204.89   13.599%   $232.753   $232.75   $232.75   $232.80  
  Purchase #7 $106.80   9.646%   $117.1019   $117.10   $117.10   $117.10  
  7 purchase totals = $981.48       $1,074.4972   $1,074.50   $1,074.50   $1,074.60