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 $62.37   6.827%   $66.628   $66.63   $66.65   $66.60  
  Purchase #2 $201.59   4.662%   $210.9881   $210.99   $211.00   $211.00  
  Purchase #3 $240.91   5.787%   $254.8515   $254.85   $254.85   $254.90  
  Purchase #4 $152.57   8.350%   $165.3096   $165.31   $165.30   $165.30  
  Purchase #5 $51.37   9.671%   $56.338   $56.34   $56.35   $56.30  
  Purchase #6 $117.85   7.250%   $126.3941   $126.39   $126.40   $126.40  
  Purchase #7 $92.39   10.191%   $101.8055   $101.81   $101.80   $101.80  
  7 purchase totals = $919.05       $982.3148   $982.32   $982.35   $982.30