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	$17.32	4.535%	$18.1055	$18.11	$18.10	$18.10
Purchase #2	$238.52	13.481%	$270.6749	$270.67	$270.65	$270.70
Purchase #3	$208.88	11.744%	$233.4109	$233.41	$233.40	$233.40
Purchase #4	$143.89	13.165%	$162.8331	$162.83	$162.85	$162.80
Purchase #5	$212.91	4.514%	$222.5208	$222.52	$222.50	$222.50
Purchase #6	$218.42	3.809%	$226.7396	$226.74	$226.75	$226.70
Purchase #7	$240.95	11.374%	$268.3557	$268.36	$268.35	$268.40
7 purchase totals =	$1,280.89		$1,402.6405	$1,402.64	$1,402.60	$1,402.60