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 $68.75   10.157%   $75.7329   $75.73   $75.75   $75.70  
  Purchase #2 $192.55   6.791%   $205.6261   $205.63   $205.65   $205.60  
  Purchase #3 $232.50   4.843%   $243.76   $243.76   $243.75   $243.80  
  Purchase #4 $107.72   6.258%   $114.4611   $114.46   $114.45   $114.50  
  Purchase #5 $82.49   5.467%   $86.9997   $87.00   $87.00   $87.00  
  Purchase #6 $169.34   12.725%   $190.8885   $190.89   $190.90   $190.90  
  Purchase #7 $51.37   7.333%   $55.137   $55.14   $55.15   $55.10  
  7 purchase totals = $904.72       $972.6053   $972.61   $972.65   $972.60