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 $38.94   13.751%   $44.2946   $44.29   $44.30   $44.30  
  Purchase #2 $198.86   7.608%   $213.9893   $213.99   $214.00   $214.00  
  Purchase #3 $232.84   7.827%   $251.0644   $251.06   $251.05   $251.10  
  Purchase #4 $248.72   4.415%   $259.701   $259.70   $259.70   $259.70  
  Purchase #5 $213.53   9.862%   $234.5883   $234.59   $234.60   $234.60  
  Purchase #6 $125.57   8.748%   $136.5549   $136.55   $136.55   $136.60  
  Purchase #7 $226.49   11.380%   $252.2646   $252.26   $252.25   $252.30  
  7 purchase totals = $1,284.95       $1,392.4571   $1,392.44   $1,392.45   $1,392.60