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 $240.85   8.359%   $260.9827   $260.98   $261.00   $261.00  
  Purchase #2 $14.87   11.225%   $16.5392   $16.54   $16.55   $16.50  
  Purchase #3 $11.37   6.799%   $12.143   $12.14   $12.15   $12.10  
  Purchase #4 $119.37   9.343%   $130.5227   $130.52   $130.50   $130.50  
  Purchase #5 $157.48   4.441%   $164.4737   $164.47   $164.45   $164.50  
  Purchase #6 $239.47   4.581%   $250.4401   $250.44   $250.45   $250.40  
  Purchase #7 $148.49   11.845%   $166.0786   $166.08   $166.10   $166.10  
  7 purchase totals = $931.90       $1,001.1800   $1,001.17   $1,001.20   $1,001.10