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 $167.48   11.348%   $186.4856   $186.49   $186.50   $186.50  
  Purchase #2 $27.41   9.170%   $29.9235   $29.92   $29.90   $29.90  
  Purchase #3 $68.96   5.539%   $72.7797   $72.78   $72.80   $72.80  
  Purchase #4 $199.81   5.811%   $211.421   $211.42   $211.40   $211.40  
  Purchase #5 $222.31   12.343%   $249.7497   $249.75   $249.75   $249.70  
  Purchase #6 $231.54   9.703%   $254.0063   $254.01   $254.00   $254.00  
  Purchase #7 $60.74   3.219%   $62.6952   $62.70   $62.70   $62.70  
  7 purchase totals = $978.25       $1,067.0610   $1,067.07   $1,067.05   $1,067.00