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 $248.78   6.784%   $265.6572   $265.66   $265.65   $265.70  
  Purchase #2 $82.98   12.730%   $93.5434   $93.54   $93.55   $93.50  
  Purchase #3 $123.89   7.204%   $132.815   $132.82   $132.80   $132.80  
  Purchase #4 $242.32   3.284%   $250.2778   $250.28   $250.30   $250.30  
  Purchase #5 $69.70   8.688%   $75.7555   $75.76   $75.75   $75.80  
  Purchase #6 $167.65   7.354%   $179.979   $179.98   $180.00   $180.00  
  Purchase #7 $180.84   6.415%   $192.4409   $192.44   $192.45   $192.40  
  7 purchase totals = $1,116.16       $1,190.4688   $1,190.48   $1,190.50   $1,190.50