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 $9.62   10.657%   $10.6452   $10.65   $10.65   $10.60  
  Purchase #2 $175.68   8.743%   $191.0397   $191.04   $191.05   $191.00  
  Purchase #3 $64.37   8.421%   $69.7906   $69.79   $69.80   $69.80  
  Purchase #4 $201.33   3.309%   $207.992   $207.99   $208.00   $208.00  
  Purchase #5 $123.55   11.123%   $137.2925   $137.29   $137.30   $137.30  
  Purchase #6 $157.25   11.319%   $175.0491   $175.05   $175.05   $175.00  
  Purchase #7 $84.65   7.270%   $90.8041   $90.80   $90.80   $90.80  
  7 purchase totals = $816.45       $882.6132   $882.61   $882.65   $882.50