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 $58.89   7.725%   $63.4393   $63.44   $63.45   $63.40  
  Purchase #2 $190.93   5.268%   $200.9882   $200.99   $201.00   $201.00  
  Purchase #3 $8.25   9.244%   $9.0126   $9.01   $9.00   $9.00  
  Purchase #4 $210.40   7.774%   $226.7565   $226.76   $226.75   $226.80  
  Purchase #5 $232.88   13.400%   $264.0859   $264.09   $264.10   $264.10  
  Purchase #6 $25.65   10.669%   $28.3866   $28.39   $28.40   $28.40  
  Purchase #7 $192.31   6.707%   $205.2082   $205.21   $205.20   $205.20  
  7 purchase totals = $919.31       $997.8773   $997.89   $997.90   $997.90