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 $147.53   7.636%   $158.7954   $158.80   $158.80   $158.80  
  Purchase #2 $43.25   12.583%   $48.6921   $48.69   $48.70   $48.70  
  Purchase #3 $219.76   3.732%   $227.9614   $227.96   $227.95   $228.00  
  Purchase #4 $96.65   11.452%   $107.7184   $107.72   $107.70   $107.70  
  Purchase #5 $182.63   13.742%   $207.727   $207.73   $207.75   $207.70  
  Purchase #6 $97.82   4.259%   $101.9862   $101.99   $102.00   $102.00  
  Purchase #7 $204.83   8.742%   $222.7362   $222.74   $222.75   $222.70  
  7 purchase totals = $992.47       $1,075.6167   $1,075.63   $1,075.65   $1,075.60