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 $237.65   11.780%   $265.6452   $265.65   $265.65   $265.60  
  Purchase #2 $67.69   9.492%   $74.1151   $74.12   $74.10   $74.10  
  Purchase #3 $30.65   4.685%   $32.086   $32.09   $32.10   $32.10  
  Purchase #4 $165.43   7.824%   $178.3732   $178.37   $178.35   $178.40  
  Purchase #5 $232.35   8.704%   $252.5737   $252.57   $252.55   $252.60  
  Purchase #6 $240.38   11.574%   $268.2016   $268.20   $268.20   $268.20  
  Purchase #7 $204.71   8.262%   $221.6231   $221.62   $221.60   $221.60  
  7 purchase totals = $1,178.86       $1,292.6179   $1,292.62   $1,292.55   $1,292.60