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 $246.82   7.722%   $265.8794   $265.88   $265.90   $265.90  
  Purchase #2 $214.42   12.298%   $240.7894   $240.79   $240.80   $240.80  
  Purchase #3 $58.38   4.365%   $60.9283   $60.93   $60.95   $60.90  
  Purchase #4 $178.59   3.330%   $184.537   $184.54   $184.55   $184.50  
  Purchase #5 $83.44   9.419%   $91.2992   $91.30   $91.30   $91.30  
  Purchase #6 $65.33   8.826%   $71.096   $71.10   $71.10   $71.10  
  Purchase #7 $8.58   10.335%   $9.4667   $9.47   $9.45   $9.50  
  7 purchase totals = $855.56       $923.9960   $924.01   $924.05   $924.00