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 $228.63   5.586%   $241.4013   $241.40   $241.40   $241.40  
  Purchase #2 $166.27   5.616%   $175.6077   $175.61   $175.60   $175.60  
  Purchase #3 $15.96   6.140%   $16.9399   $16.94   $16.95   $16.90  
  Purchase #4 $113.30   10.182%   $124.8362   $124.84   $124.85   $124.80  
  Purchase #5 $164.98   9.604%   $180.8247   $180.82   $180.80   $180.80  
  Purchase #6 $118.52   3.171%   $122.2783   $122.28   $122.30   $122.30  
  Purchase #7 $196.96   4.285%   $205.3997   $205.40   $205.40   $205.40  
  7 purchase totals = $1,004.62       $1,067.2878   $1,067.29   $1,067.30   $1,067.20