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 $168.58   9.465%   $184.5361   $184.54   $184.55   $184.50  
  Purchase #2 $174.90   10.716%   $193.6423   $193.64   $193.65   $193.60  
  Purchase #3 $193.35   5.246%   $203.4931   $203.49   $203.50   $203.50  
  Purchase #4 $216.58   10.186%   $238.6408   $238.64   $238.65   $238.60  
  Purchase #5 $199.97   13.388%   $226.742   $226.74   $226.75   $226.70  
  Purchase #6 $91.95   7.663%   $98.9961   $99.00   $99.00   $99.00  
  Purchase #7 $199.61   7.403%   $214.3871   $214.39   $214.40   $214.40  
  7 purchase totals = $1,244.94       $1,360.4375   $1,360.44   $1,360.50   $1,360.30