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 $37.29   10.555%   $41.226   $41.23   $41.25   $41.20  
  Purchase #2 $176.29   8.574%   $191.4051   $191.41   $191.40   $191.40  
  Purchase #3 $188.51   5.499%   $198.8762   $198.88   $198.90   $198.90  
  Purchase #4 $246.59   8.743%   $268.1494   $268.15   $268.15   $268.10  
  Purchase #5 $24.78   8.732%   $26.9438   $26.94   $26.95   $26.90  
  Purchase #6 $175.66   11.512%   $195.882   $195.88   $195.90   $195.90  
  Purchase #7 $72.26   10.262%   $79.6753   $79.68   $79.70   $79.70  
  7 purchase totals = $921.38       $1,002.1578   $1,002.17   $1,002.25   $1,002.10