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 $61.43   12.326%   $69.0019   $69.00   $69.00   $69.00  
  Purchase #2 $52.85   12.683%   $59.553   $59.55   $59.55   $59.60  
  Purchase #3 $186.25   7.177%   $199.6172   $199.62   $199.60   $199.60  
  Purchase #4 $196.75   9.135%   $214.7231   $214.72   $214.70   $214.70  
  Purchase #5 $204.44   13.863%   $232.7815   $232.78   $232.80   $232.80  
  Purchase #6 $6.85   12.375%   $7.6977   $7.70   $7.70   $7.70  
  Purchase #7 $10.49   9.319%   $11.4676   $11.47   $11.45   $11.50  
  7 purchase totals = $719.06       $794.8420   $794.84   $794.80   $794.90