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 $104.48   11.868%   $116.8797   $116.88   $116.90   $116.90  
  Purchase #2 $187.40   10.415%   $206.9177   $206.92   $206.90   $206.90  
  Purchase #3 $250.73   10.608%   $277.3274   $277.33   $277.35   $277.30  
  Purchase #4 $164.63   6.752%   $175.7458   $175.75   $175.75   $175.70  
  Purchase #5 $132.84   7.842%   $143.2573   $143.26   $143.25   $143.30  
  Purchase #6 $88.56   11.254%   $98.5265   $98.53   $98.55   $98.50  
  Purchase #7 $75.71   10.294%   $83.5036   $83.50   $83.50   $83.50  
  7 purchase totals = $1,004.35       $1,102.1580   $1,102.17   $1,102.20   $1,102.10