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 $153.63   6.732%   $163.9724   $163.97   $163.95   $164.00  
  Purchase #2 $32.76   11.263%   $36.4498   $36.45   $36.45   $36.40  
  Purchase #3 $202.45   7.270%   $217.1681   $217.17   $217.15   $217.20  
  Purchase #4 $242.43   11.341%   $269.924   $269.92   $269.90   $269.90  
  Purchase #5 $50.56   12.620%   $56.9407   $56.94   $56.95   $56.90  
  Purchase #6 $118.34   5.861%   $125.2759   $125.28   $125.30   $125.30  
  Purchase #7 $205.73   12.298%   $231.0307   $231.03   $231.05   $231.00  
  7 purchase totals = $1,005.90       $1,100.7616   $1,100.76   $1,100.75   $1,100.70