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 $61.76   12.209%   $69.3003   $69.30   $69.30   $69.30  
  Purchase #2 $62.83   8.565%   $68.2114   $68.21   $68.20   $68.20  
  Purchase #3 $183.46   12.433%   $206.2696   $206.27   $206.25   $206.30  
  Purchase #4 $195.54   13.682%   $222.2938   $222.29   $222.30   $222.30  
  Purchase #5 $86.47   10.279%   $95.3583   $95.36   $95.35   $95.40  
  Purchase #6 $232.58   10.267%   $256.459   $256.46   $256.45   $256.50  
  Purchase #7 $241.83   5.436%   $254.9759   $254.98   $255.00   $255.00  
  7 purchase totals = $1,064.47       $1,172.8683   $1,172.87   $1,172.85   $1,173.00