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 $65.29   5.823%   $69.0918   $69.09   $69.10   $69.10  
  Purchase #2 $48.74   3.745%   $50.5653   $50.57   $50.55   $50.60  
  Purchase #3 $44.68   3.856%   $46.4029   $46.40   $46.40   $46.40  
  Purchase #4 $23.90   8.343%   $25.894   $25.89   $25.90   $25.90  
  Purchase #5 $167.91   7.500%   $180.5033   $180.50   $180.50   $180.50  
  Purchase #6 $10.49   3.762%   $10.8846   $10.88   $10.90   $10.90  
  Purchase #7 $203.43   9.502%   $222.7599   $222.76   $222.75   $222.80  
  7 purchase totals = $564.44       $606.1018   $606.09   $606.10   $606.20