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 $32.27   8.416%   $34.9858   $34.99   $35.00   $35.00  
  Purchase #2 $103.39   4.142%   $107.6724   $107.67   $107.65   $107.70  
  Purchase #3 $151.95   7.560%   $163.4374   $163.44   $163.45   $163.40  
  Purchase #4 $199.45   10.870%   $221.1302   $221.13   $221.15   $221.10  
  Purchase #5 $184.46   11.627%   $205.9072   $205.91   $205.90   $205.90  
  Purchase #6 $22.98   4.552%   $24.026   $24.03   $24.05   $24.00  
  Purchase #7 $216.69   10.630%   $239.7241   $239.72   $239.70   $239.70  
  7 purchase totals = $911.19       $996.8831   $996.89   $996.90   $996.80