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 $178.90   13.230%   $202.5685   $202.57   $202.55   $202.60  
  Purchase #2 $208.27   5.410%   $219.5374   $219.54   $219.55   $219.50  
  Purchase #3 $55.36   4.354%   $57.7704   $57.77   $57.75   $57.80  
  Purchase #4 $224.57   4.629%   $234.9653   $234.97   $234.95   $235.00  
  Purchase #5 $143.84   12.344%   $161.5956   $161.60   $161.60   $161.60  
  Purchase #6 $163.37   8.473%   $177.2123   $177.21   $177.20   $177.20  
  Purchase #7 $20.84   5.577%   $22.0022   $22.00   $22.00   $22.00  
  7 purchase totals = $995.15       $1,075.6517   $1,075.66   $1,075.60   $1,075.70