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 $41.51   11.644%   $46.3434   $46.34   $46.35   $46.30  
  Purchase #2 $120.73   12.599%   $135.9408   $135.94   $135.95   $135.90  
  Purchase #3 $207.84   7.328%   $223.0705   $223.07   $223.05   $223.10  
  Purchase #4 $205.67   4.499%   $214.9231   $214.92   $214.90   $214.90  
  Purchase #5 $74.80   11.568%   $83.4529   $83.45   $83.45   $83.50  
  Purchase #6 $104.93   7.119%   $112.4   $112.40   $112.40   $112.40  
  Purchase #7 $161.41   5.477%   $170.2504   $170.25   $170.25   $170.30  
  7 purchase totals = $916.89       $986.3811   $986.37   $986.35   $986.40