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 $184.62   12.441%   $207.5886   $207.59   $207.60   $207.60  
  Purchase #2 $206.35   5.584%   $217.8726   $217.87   $217.85   $217.90  
  Purchase #3 $90.89   12.335%   $102.1013   $102.10   $102.10   $102.10  
  Purchase #4 $51.87   9.261%   $56.6737   $56.67   $56.65   $56.70  
  Purchase #5 $33.47   6.380%   $35.6054   $35.61   $35.60   $35.60  
  Purchase #6 $244.57   10.226%   $269.5797   $269.58   $269.60   $269.60  
  Purchase #7 $15.78   6.730%   $16.842   $16.84   $16.85   $16.80  
  7 purchase totals = $827.55       $906.2633   $906.26   $906.25   $906.30