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   6.176%   $69.3223   $69.32   $69.30   $69.30  
  Purchase #2 $167.72   11.305%   $186.6807   $186.68   $186.70   $186.70  
  Purchase #3 $60.96   10.224%   $67.1926   $67.19   $67.20   $67.20  
  Purchase #4 $112.60   5.608%   $118.9146   $118.91   $118.90   $118.90  
  Purchase #5 $68.76   13.581%   $78.0983   $78.10   $78.10   $78.10  
  Purchase #6 $6.87   11.776%   $7.679   $7.68   $7.70   $7.70  
  Purchase #7 $144.39   10.190%   $159.1033   $159.10   $159.10   $159.10  
  7 purchase totals = $626.59       $686.9908   $686.98   $687.00   $687.00