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 $174.76   10.835%   $193.6952   $193.70   $193.70   $193.70  
  Purchase #2 $239.56   12.627%   $269.8092   $269.81   $269.80   $269.80  
  Purchase #3 $43.55   8.827%   $47.3942   $47.39   $47.40   $47.40  
  Purchase #4 $207.96   3.323%   $214.8705   $214.87   $214.85   $214.90  
  Purchase #5 $186.44   9.233%   $203.654   $203.65   $203.65   $203.70  
  Purchase #6 $148.58   11.177%   $165.1868   $165.19   $165.20   $165.20  
  Purchase #7 $131.64   13.788%   $149.7905   $149.79   $149.80   $149.80  
  7 purchase totals = $1,132.49       $1,244.4004   $1,244.40   $1,244.40   $1,244.50