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 $147.82   4.186%   $154.0077   $154.01   $154.00   $154.00  
  Purchase #2 $176.55   11.869%   $197.5047   $197.50   $197.50   $197.50  
  Purchase #3 $135.99   11.265%   $151.3093   $151.31   $151.30   $151.30  
  Purchase #4 $161.77   7.254%   $173.5048   $173.50   $173.50   $173.50  
  Purchase #5 $88.74   10.107%   $97.709   $97.71   $97.70   $97.70  
  Purchase #6 $119.78   3.411%   $123.8657   $123.87   $123.85   $123.90  
  Purchase #7 $98.97   6.555%   $105.4575   $105.46   $105.45   $105.50  
  7 purchase totals = $929.62       $1,003.3587   $1,003.36   $1,003.30   $1,003.40