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 $63.94   5.152%   $67.2342   $67.23   $67.25   $67.20  
  Purchase #2 $239.29   4.600%   $250.2973   $250.30   $250.30   $250.30  
  Purchase #3 $109.89   12.128%   $123.2175   $123.22   $123.20   $123.20  
  Purchase #4 $14.44   3.775%   $14.9851   $14.99   $15.00   $15.00  
  Purchase #5 $165.54   11.663%   $184.8469   $184.85   $184.85   $184.80  
  Purchase #6 $197.78   9.242%   $216.0588   $216.06   $216.05   $216.10  
  Purchase #7 $189.90   5.807%   $200.9275   $200.93   $200.95   $200.90  
  7 purchase totals = $980.78       $1,057.5673   $1,057.58   $1,057.60   $1,057.50