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 $224.62   10.511%   $248.2298   $248.23   $248.25   $248.20  
  Purchase #2 $211.62   13.731%   $240.6775   $240.68   $240.70   $240.70  
  Purchase #3 $190.37   3.260%   $196.5761   $196.58   $196.60   $196.60  
  Purchase #4 $59.46   9.153%   $64.9024   $64.90   $64.90   $64.90  
  Purchase #5 $87.93   10.843%   $97.4642   $97.46   $97.45   $97.50  
  Purchase #6 $74.26   4.658%   $77.719   $77.72   $77.70   $77.70  
  Purchase #7 $34.58   12.689%   $38.9679   $38.97   $38.95   $39.00  
  7 purchase totals = $882.84       $964.5369   $964.54   $964.55   $964.60