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 $163.70   10.341%   $180.6282   $180.63   $180.65   $180.60  
  Purchase #2 $151.41   8.541%   $164.3419   $164.34   $164.35   $164.30  
  Purchase #3 $201.33   11.352%   $224.185   $224.19   $224.20   $224.20  
  Purchase #4 $143.64   8.857%   $156.3622   $156.36   $156.35   $156.40  
  Purchase #5 $208.54   8.392%   $226.0407   $226.04   $226.05   $226.00  
  Purchase #6 $43.84   9.118%   $47.8373   $47.84   $47.85   $47.80  
  Purchase #7 $140.69   5.211%   $148.0214   $148.02   $148.00   $148.00  
  7 purchase totals = $1,053.15       $1,147.4167   $1,147.42   $1,147.45   $1,147.30