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 $151.59   6.257%   $161.075   $161.08   $161.10   $161.10  
  Purchase #2 $173.30   10.193%   $190.9645   $190.96   $190.95   $191.00  
  Purchase #3 $52.25   10.679%   $57.8298   $57.83   $57.85   $57.80  
  Purchase #4 $208.27   12.596%   $234.5037   $234.50   $234.50   $234.50  
  Purchase #5 $198.90   13.676%   $226.1016   $226.10   $226.10   $226.10  
  Purchase #6 $30.45   13.704%   $34.6229   $34.62   $34.60   $34.60  
  Purchase #7 $154.68   9.840%   $169.9005   $169.90   $169.90   $169.90  
  7 purchase totals = $969.44       $1,074.9980   $1,074.99   $1,075.00   $1,075.00