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	$136.95	3.416%	$141.6282	$141.63	$141.65	$141.60
Purchase #2	$210.94	13.224%	$238.8347	$238.83	$238.85	$238.80
Purchase #3	$52.89	12.117%	$59.2987	$59.30	$59.30	$59.30
Purchase #4	$209.75	11.434%	$233.7328	$233.73	$233.75	$233.70
Purchase #5	$7.63	7.716%	$8.2187	$8.22	$8.20	$8.20
Purchase #6	$10.36	7.142%	$11.0999	$11.10	$11.10	$11.10
Purchase #7	$75.62	3.692%	$78.4119	$78.41	$78.40	$78.40
7 purchase totals =	$704.14		$771.2249	$771.22	$771.25	$771.10