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 $183.91   9.619%   $201.6003   $201.60   $201.60   $201.60  
  Purchase #2 $13.50   8.623%   $14.6641   $14.66   $14.65   $14.70  
  Purchase #3 $59.83   12.691%   $67.423   $67.42   $67.40   $67.40  
  Purchase #4 $16.72   11.117%   $18.5788   $18.58   $18.60   $18.60  
  Purchase #5 $53.50   10.213%   $58.964   $58.96   $58.95   $59.00  
  Purchase #6 $183.37   12.523%   $206.3334   $206.33   $206.35   $206.30  
  Purchase #7 $203.61   7.628%   $219.1414   $219.14   $219.15   $219.10  
  7 purchase totals = $714.44       $786.7050   $786.69   $786.70   $786.70