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 $59.49   11.258%   $66.1874   $66.19   $66.20   $66.20  
  Purchase #2 $192.73   6.495%   $205.2478   $205.25   $205.25   $205.20  
  Purchase #3 $151.30   8.581%   $164.2831   $164.28   $164.30   $164.30  
  Purchase #4 $212.78   9.705%   $233.4303   $233.43   $233.45   $233.40  
  Purchase #5 $201.99   9.632%   $221.4457   $221.45   $221.45   $221.40  
  Purchase #6 $74.90   8.485%   $81.2553   $81.26   $81.25   $81.30  
  Purchase #7 $214.92   8.704%   $233.6266   $233.63   $233.65   $233.60  
  7 purchase totals = $1,108.11       $1,205.4762   $1,205.49   $1,205.55   $1,205.40