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 $239.57   11.563%   $267.2715   $267.27   $267.25   $267.30  
  Purchase #2 $87.79   9.137%   $95.8114   $95.81   $95.80   $95.80  
  Purchase #3 $90.96   6.198%   $96.5977   $96.60   $96.60   $96.60  
  Purchase #4 $174.73   10.413%   $192.9246   $192.92   $192.90   $192.90  
  Purchase #5 $205.65   10.723%   $227.7018   $227.70   $227.70   $227.70  
  Purchase #6 $41.58   10.856%   $46.0939   $46.09   $46.10   $46.10  
  Purchase #7 $50.42   10.531%   $55.7297   $55.73   $55.75   $55.70  
  7 purchase totals = $890.70       $982.1306   $982.12   $982.10   $982.10