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 $67.48   13.643%   $76.6863   $76.69   $76.70   $76.70  
  Purchase #2 $237.72   5.613%   $251.0632   $251.06   $251.05   $251.10  
  Purchase #3 $171.57   8.319%   $185.8429   $185.84   $185.85   $185.80  
  Purchase #4 $160.80   11.320%   $179.0026   $179.00   $179.00   $179.00  
  Purchase #5 $235.78   6.570%   $251.2707   $251.27   $251.25   $251.30  
  Purchase #6 $85.64   6.237%   $90.9814   $90.98   $91.00   $91.00  
  Purchase #7 $204.57   11.344%   $227.7764   $227.78   $227.80   $227.80  
  7 purchase totals = $1,163.56       $1,262.6235   $1,262.62   $1,262.65   $1,262.70