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 $53.84   9.722%   $59.0743   $59.07   $59.05   $59.10  
  Purchase #2 $229.65   5.373%   $241.9891   $241.99   $242.00   $242.00  
  Purchase #3 $166.59   13.240%   $188.6465   $188.65   $188.65   $188.60  
  Purchase #4 $152.58   4.535%   $159.4995   $159.50   $159.50   $159.50  
  Purchase #5 $156.32   7.469%   $167.9955   $168.00   $168.00   $168.00  
  Purchase #6 $85.74   6.597%   $91.3963   $91.40   $91.40   $91.40  
  Purchase #7 $194.64   6.114%   $206.5403   $206.54   $206.55   $206.50  
  7 purchase totals = $1,039.36       $1,115.1415   $1,115.15   $1,115.15   $1,115.10