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	$65.88	7.360%	$70.7288	$70.73	$70.75	$70.70
Purchase #2	$16.28	13.198%	$18.4286	$18.43	$18.45	$18.40
Purchase #3	$64.81	12.402%	$72.8477	$72.85	$72.85	$72.80
Purchase #4	$178.29	11.262%	$198.369	$198.37	$198.35	$198.40
Purchase #5	$224.29	7.230%	$240.5062	$240.51	$240.50	$240.50
Purchase #6	$150.79	7.247%	$161.7178	$161.72	$161.70	$161.70
Purchase #7	$53.97	13.498%	$61.2549	$61.25	$61.25	$61.30
7 purchase totals =	$754.31		$823.8530	$823.86	$823.85	$823.80