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	$141.47	3.831%	$146.8897	$146.89	$146.90	$146.90
Purchase #2	$154.92	4.705%	$162.209	$162.21	$162.20	$162.20
Purchase #3	$51.36	7.173%	$55.0441	$55.04	$55.05	$55.00
Purchase #4	$6.52	13.623%	$7.4082	$7.41	$7.40	$7.40
Purchase #5	$88.71	12.620%	$99.9052	$99.91	$99.90	$99.90
Purchase #6	$141.69	8.587%	$153.8569	$153.86	$153.85	$153.90
Purchase #7	$143.49	11.186%	$159.5408	$159.54	$159.55	$159.50
7 purchase totals =	$728.16		$784.8539	$784.86	$784.85	$784.80