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 $246.30   8.752%   $267.8562   $267.86   $267.85   $267.90  
  Purchase #2 $202.56   12.332%   $227.5397   $227.54   $227.55   $227.50  
  Purchase #3 $226.47   13.497%   $257.0367   $257.04   $257.05   $257.00  
  Purchase #4 $234.26   8.216%   $253.5068   $253.51   $253.50   $253.50  
  Purchase #5 $107.34   6.273%   $114.0734   $114.07   $114.05   $114.10  
  Purchase #6 $186.52   13.739%   $212.146   $212.15   $212.15   $212.10  
  Purchase #7 $211.90   7.539%   $227.8751   $227.88   $227.90   $227.90  
  7 purchase totals = $1,415.35       $1,560.0339   $1,560.05   $1,560.05   $1,560.00