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 $165.83   11.711%   $185.2504   $185.25   $185.25   $185.30  
  Purchase #2 $175.90   9.485%   $192.5841   $192.58   $192.60   $192.60  
  Purchase #3 $150.32   9.797%   $165.0469   $165.05   $165.05   $165.00  
  Purchase #4 $203.54   9.217%   $222.3003   $222.30   $222.30   $222.30  
  Purchase #5 $239.88   11.697%   $267.9388   $267.94   $267.95   $267.90  
  Purchase #6 $109.41   5.453%   $115.3761   $115.38   $115.40   $115.40  
  Purchase #7 $203.30   4.303%   $212.048   $212.05   $212.05   $212.00  
  7 purchase totals = $1,248.18       $1,360.5446   $1,360.55   $1,360.60   $1,360.50