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 $226.84   10.667%   $251.037   $251.04   $251.05   $251.00  
  Purchase #2 $242.99   7.813%   $261.9748   $261.97   $261.95   $262.00  
  Purchase #3 $124.85   5.555%   $131.7854   $131.79   $131.80   $131.80  
  Purchase #4 $34.99   3.708%   $36.2874   $36.29   $36.30   $36.30  
  Purchase #5 $119.56   4.488%   $124.9259   $124.93   $124.95   $124.90  
  Purchase #6 $24.44   5.757%   $25.847   $25.85   $25.85   $25.80  
  Purchase #7 $201.30   3.155%   $207.651   $207.65   $207.65   $207.70  
  7 purchase totals = $974.97       $1,039.5085   $1,039.52   $1,039.55   $1,039.50