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 $162.69   12.629%   $183.2361   $183.24   $183.25   $183.20  
  Purchase #2 $34.49   9.123%   $37.6365   $37.64   $37.65   $37.60  
  Purchase #3 $186.52   10.857%   $206.7705   $206.77   $206.75   $206.80  
  Purchase #4 $68.63   6.659%   $73.2001   $73.20   $73.20   $73.20  
  Purchase #5 $147.44   11.627%   $164.5828   $164.58   $164.60   $164.60  
  Purchase #6 $235.27   7.699%   $253.3834   $253.38   $253.40   $253.40  
  Purchase #7 $43.84   8.356%   $47.5033   $47.50   $47.50   $47.50  
  7 purchase totals = $878.88       $966.3127   $966.31   $966.35   $966.30