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 $62.32   11.710%   $69.6177   $69.62   $69.60   $69.60  
  Purchase #2 $169.60   8.296%   $183.67   $183.67   $183.65   $183.70  
  Purchase #3 $220.69   8.124%   $238.6189   $238.62   $238.60   $238.60  
  Purchase #4 $131.37   4.804%   $137.681   $137.68   $137.70   $137.70  
  Purchase #5 $60.74   4.608%   $63.5389   $63.54   $63.55   $63.50  
  Purchase #6 $247.57   13.821%   $281.7866   $281.79   $281.80   $281.80  
  Purchase #7 $118.76   13.325%   $134.5848   $134.58   $134.60   $134.60  
  7 purchase totals = $1,011.05       $1,109.4979   $1,109.50   $1,109.50   $1,109.50