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 $205.41   11.452%   $228.9336   $228.93   $228.95   $228.90  
  Purchase #2 $250.37   13.447%   $284.0373   $284.04   $284.05   $284.00  
  Purchase #3 $81.87   8.731%   $89.0181   $89.02   $89.00   $89.00  
  Purchase #4 $84.57   11.743%   $94.5011   $94.50   $94.50   $94.50  
  Purchase #5 $28.81   13.710%   $32.7599   $32.76   $32.75   $32.80  
  Purchase #6 $129.42   5.640%   $136.7193   $136.72   $136.70   $136.70  
  Purchase #7 $162.50   12.168%   $182.273   $182.27   $182.25   $182.30  
  7 purchase totals = $942.95       $1,048.2423   $1,048.24   $1,048.20   $1,048.20