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 $207.47   5.401%   $218.6755   $218.68   $218.70   $218.70  
  Purchase #2 $66.97   8.275%   $72.5118   $72.51   $72.50   $72.50  
  Purchase #3 $20.76   5.392%   $21.8794   $21.88   $21.90   $21.90  
  Purchase #4 $247.74   7.745%   $266.9275   $266.93   $266.95   $266.90  
  Purchase #5 $124.70   6.638%   $132.9776   $132.98   $133.00   $133.00  
  Purchase #6 $72.51   13.262%   $82.1263   $82.13   $82.15   $82.10  
  Purchase #7 $220.65   12.809%   $248.9131   $248.91   $248.90   $248.90  
  7 purchase totals = $960.80       $1,044.0112   $1,044.02   $1,044.10   $1,044.00