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 $240.72   11.827%   $269.19   $269.19   $269.20   $269.20  
  Purchase #2 $201.35   3.581%   $208.5603   $208.56   $208.55   $208.60  
  Purchase #3 $156.97   12.484%   $176.5661   $176.57   $176.55   $176.60  
  Purchase #4 $150.49   4.321%   $156.9927   $156.99   $157.00   $157.00  
  Purchase #5 $226.64   8.551%   $246.02   $246.02   $246.00   $246.00  
  Purchase #6 $212.67   3.757%   $220.66   $220.66   $220.65   $220.70  
  Purchase #7 $206.37   13.406%   $234.036   $234.04   $234.05   $234.00  
  7 purchase totals = $1,395.21       $1,512.0251   $1,512.03   $1,512.00   $1,512.10