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	$54.31	5.420%	$57.2536	$57.25	$57.25	$57.30
Purchase #2	$47.38	5.216%	$49.8513	$49.85	$49.85	$49.90
Purchase #3	$51.89	6.667%	$55.3495	$55.35	$55.35	$55.30
Purchase #4	$90.26	5.122%	$94.8831	$94.88	$94.90	$94.90
Purchase #5	$59.39	6.399%	$63.1904	$63.19	$63.20	$63.20
Purchase #6	$35.67	12.595%	$40.1626	$40.16	$40.15	$40.20
Purchase #7	$162.82	9.391%	$178.1104	$178.11	$178.10	$178.10
7 purchase totals =	$501.72		$538.8009	$538.79	$538.80	$538.90