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 $68.39   11.279%   $76.1037   $76.10   $76.10   $76.10  
  Purchase #2 $98.66   6.290%   $104.8657   $104.87   $104.85   $104.90  
  Purchase #3 $178.58   11.174%   $198.5345   $198.53   $198.55   $198.50  
  Purchase #4 $5.34   7.386%   $5.7344   $5.73   $5.75   $5.70  
  Purchase #5 $243.61   6.831%   $260.251   $260.25   $260.25   $260.30  
  Purchase #6 $105.43   7.147%   $112.9651   $112.97   $112.95   $113.00  
  Purchase #7 $8.41   11.331%   $9.3629   $9.36   $9.35   $9.40  
  7 purchase totals = $708.42       $767.8173   $767.81   $767.80   $767.90