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	$48.89	13.630%	$55.5537	$55.55	$55.55	$55.60
Purchase #2	$159.53	4.813%	$167.2082	$167.21	$167.20	$167.20
Purchase #3	$56.93	8.803%	$61.9415	$61.94	$61.95	$61.90
Purchase #4	$17.96	5.179%	$18.8901	$18.89	$18.90	$18.90
Purchase #5	$108.56	5.545%	$114.5797	$114.58	$114.60	$114.60
Purchase #6	$162.98	13.710%	$185.3246	$185.32	$185.30	$185.30
Purchase #7	$42.66	9.542%	$46.7306	$46.73	$46.75	$46.70
7 purchase totals =	$597.51		$650.2284	$650.22	$650.25	$650.20