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	$140.81	12.454%	$158.3465	$158.35	$158.35	$158.30
Purchase #2	$250.88	7.316%	$269.2344	$269.23	$269.25	$269.20
Purchase #3	$45.33	10.571%	$50.1218	$50.12	$50.10	$50.10
Purchase #4	$68.78	3.221%	$70.9954	$71.00	$71.00	$71.00
Purchase #5	$93.96	11.289%	$104.5671	$104.57	$104.55	$104.60
Purchase #6	$94.50	5.793%	$99.9744	$99.97	$99.95	$100.00
Purchase #7	$224.34	6.494%	$238.9086	$238.91	$238.90	$238.90
7 purchase totals =	$918.60		$992.1482	$992.15	$992.10	$992.10