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 $234.30   12.135%   $262.7323   $262.73   $262.75   $262.70  
  Purchase #2 $232.94   4.169%   $242.6513   $242.65   $242.65   $242.70  
  Purchase #3 $127.96   4.326%   $133.4955   $133.50   $133.50   $133.50  
  Purchase #4 $211.48   12.797%   $238.5431   $238.54   $238.55   $238.50  
  Purchase #5 $45.84   3.317%   $47.3605   $47.36   $47.35   $47.40  
  Purchase #6 $180.50   3.869%   $187.4835   $187.48   $187.50   $187.50  
  Purchase #7 $207.51   3.318%   $214.3952   $214.40   $214.40   $214.40  
  7 purchase totals = $1,240.53       $1,326.6614   $1,326.66   $1,326.70   $1,326.70