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 $192.49   4.466%   $201.0866   $201.09   $201.10   $201.10  
  Purchase #2 $79.95   3.480%   $82.7323   $82.73   $82.75   $82.70  
  Purchase #3 $112.27   4.149%   $116.9281   $116.93   $116.95   $116.90  
  Purchase #4 $27.43   7.647%   $29.5276   $29.53   $29.55   $29.50  
  Purchase #5 $147.59   11.513%   $164.582   $164.58   $164.60   $164.60  
  Purchase #6 $28.85   8.694%   $31.3582   $31.36   $31.35   $31.40  
  Purchase #7 $156.57   8.661%   $170.1305   $170.13   $170.15   $170.10  
  7 purchase totals = $745.15       $796.3453   $796.35   $796.45   $796.30