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	$73.87	5.209%	$77.7179	$77.72	$77.70	$77.70
Purchase #2	$195.99	11.374%	$218.2819	$218.28	$218.30	$218.30
Purchase #3	$50.56	5.870%	$53.5279	$53.53	$53.55	$53.50
Purchase #4	$71.57	9.636%	$78.4665	$78.47	$78.45	$78.50
Purchase #5	$88.31	13.712%	$100.4191	$100.42	$100.40	$100.40
Purchase #6	$109.45	5.744%	$115.7368	$115.74	$115.75	$115.70
Purchase #7	$65.71	9.264%	$71.7974	$71.80	$71.80	$71.80
7 purchase totals =	$655.46		$715.9475	$715.96	$715.95	$715.90