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 $62.28   10.620%   $68.8941   $68.89   $68.90   $68.90  
  Purchase #2 $219.56   6.835%   $234.5669   $234.57   $234.55   $234.60  
  Purchase #3 $238.77   6.814%   $255.0398   $255.04   $255.05   $255.00  
  Purchase #4 $219.57   6.592%   $234.0441   $234.04   $234.05   $234.00  
  Purchase #5 $179.58   4.378%   $187.442   $187.44   $187.45   $187.40  
  Purchase #6 $92.63   6.583%   $98.7278   $98.73   $98.75   $98.70  
  Purchase #7 $146.89   11.567%   $163.8808   $163.88   $163.90   $163.90  
  7 purchase totals = $1,159.28       $1,242.5955   $1,242.59   $1,242.65   $1,242.50