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	$53.74	9.864%	$59.0409	$59.04	$59.05	$59.00
Purchase #2	$161.81	13.590%	$183.8	$183.80	$183.80	$183.80
Purchase #3	$209.45	10.394%	$231.2202	$231.22	$231.20	$231.20
Purchase #4	$165.54	3.424%	$171.2081	$171.21	$171.20	$171.20
Purchase #5	$35.41	8.677%	$38.4825	$38.48	$38.50	$38.50
Purchase #6	$17.62	7.229%	$18.8937	$18.89	$18.90	$18.90
Purchase #7	$124.98	9.471%	$136.8169	$136.82	$136.80	$136.80
7 purchase totals =	$768.55		$839.4623	$839.46	$839.45	$839.40