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 $198.90   3.226%   $205.3165   $205.32   $205.30   $205.30  
  Purchase #2 $29.49   8.535%   $32.007   $32.01   $32.00   $32.00  
  Purchase #3 $204.33   9.329%   $223.3919   $223.39   $223.40   $223.40  
  Purchase #4 $105.61   13.416%   $119.7786   $119.78   $119.80   $119.80  
  Purchase #5 $214.28   7.567%   $230.4946   $230.49   $230.50   $230.50  
  Purchase #6 $180.33   13.821%   $205.2534   $205.25   $205.25   $205.30  
  Purchase #7 $161.54   10.354%   $178.2659   $178.27   $178.25   $178.30  
  7 purchase totals = $1,094.48       $1,194.5079   $1,194.51   $1,194.50   $1,194.60