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 $147.84   10.633%   $163.5598   $163.56   $163.55   $163.60  
  Purchase #2 $249.34   3.354%   $257.7029   $257.70   $257.70   $257.70  
  Purchase #3 $135.78   11.720%   $151.6934   $151.69   $151.70   $151.70  
  Purchase #4 $33.50   3.573%   $34.697   $34.70   $34.70   $34.70  
  Purchase #5 $228.89   11.526%   $255.2719   $255.27   $255.25   $255.30  
  Purchase #6 $222.80   8.811%   $242.4309   $242.43   $242.45   $242.40  
  Purchase #7 $245.46   5.472%   $258.8916   $258.89   $258.90   $258.90  
  7 purchase totals = $1,263.61       $1,364.2475   $1,364.24   $1,364.25   $1,364.30