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 $233.50   11.699%   $260.8172   $260.82   $260.80   $260.80  
  Purchase #2 $165.57   5.482%   $174.6465   $174.65   $174.65   $174.60  
  Purchase #3 $188.49   9.606%   $206.5963   $206.60   $206.60   $206.60  
  Purchase #4 $159.80   9.659%   $175.2351   $175.24   $175.25   $175.20  
  Purchase #5 $142.56   9.691%   $156.3755   $156.38   $156.40   $156.40  
  Purchase #6 $186.71   5.826%   $197.5877   $197.59   $197.60   $197.60  
  Purchase #7 $23.87   5.766%   $25.2463   $25.25   $25.25   $25.20  
  7 purchase totals = $1,100.50       $1,196.5046   $1,196.53   $1,196.55   $1,196.40