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 $67.61   13.335%   $76.6258   $76.63   $76.65   $76.60  
  Purchase #2 $121.54   6.639%   $129.609   $129.61   $129.60   $129.60  
  Purchase #3 $220.95   4.164%   $230.1504   $230.15   $230.15   $230.20  
  Purchase #4 $45.59   11.145%   $50.671   $50.67   $50.65   $50.70  
  Purchase #5 $79.34   10.313%   $87.5223   $87.52   $87.50   $87.50  
  Purchase #6 $248.63   8.431%   $269.592   $269.59   $269.60   $269.60  
  Purchase #7 $53.84   11.426%   $59.9918   $59.99   $60.00   $60.00  
  7 purchase totals = $837.50       $904.1623   $904.16   $904.15   $904.20