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	$36.45	10.818%	$40.3932	$40.39	$40.40	$40.40
Purchase #2	$46.38	13.607%	$52.6909	$52.69	$52.70	$52.70
Purchase #3	$152.80	4.146%	$159.1351	$159.14	$159.15	$159.10
Purchase #4	$125.44	12.318%	$140.8917	$140.89	$140.90	$140.90
Purchase #5	$118.40	10.629%	$130.9847	$130.98	$131.00	$131.00
Purchase #6	$238.79	12.612%	$268.9062	$268.91	$268.90	$268.90
Purchase #7	$63.36	12.819%	$71.4821	$71.48	$71.50	$71.50
7 purchase totals =	$781.62		$864.4839	$864.48	$864.55	$864.50