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	$32.91	6.827%	$35.1568	$35.16	$35.15	$35.20
Purchase #2	$28.46	9.729%	$31.2289	$31.23	$31.25	$31.20
Purchase #3	$58.93	4.232%	$61.4239	$61.42	$61.40	$61.40
Purchase #4	$117.34	5.190%	$123.4299	$123.43	$123.45	$123.40
Purchase #5	$245.53	3.817%	$254.9019	$254.90	$254.90	$254.90
Purchase #6	$195.68	7.768%	$210.8804	$210.88	$210.90	$210.90
Purchase #7	$92.40	13.149%	$104.5497	$104.55	$104.55	$104.50
7 purchase totals =	$771.25		$821.5715	$821.57	$821.60	$821.50