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	$221.27	8.335%	$239.7129	$239.71	$239.70	$239.70
Purchase #2	$101.95	7.179%	$109.269	$109.27	$109.25	$109.30
Purchase #3	$97.51	11.836%	$109.0513	$109.05	$109.05	$109.10
Purchase #4	$245.60	7.219%	$263.3299	$263.33	$263.35	$263.30
Purchase #5	$123.98	13.513%	$140.7334	$140.73	$140.75	$140.70
Purchase #6	$56.91	4.615%	$59.5364	$59.54	$59.55	$59.50
Purchase #7	$172.33	3.777%	$178.8389	$178.84	$178.85	$178.80
7 purchase totals =	$1,019.55		$1,100.4718	$1,100.47	$1,100.50	$1,100.40