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	$86.73	11.750%	$96.9208	$96.92	$96.90	$96.90
Purchase #2	$141.90	10.109%	$156.2447	$156.24	$156.25	$156.20
Purchase #3	$35.98	7.525%	$38.6875	$38.69	$38.70	$38.70
Purchase #4	$120.46	3.674%	$124.8857	$124.89	$124.90	$124.90
Purchase #5	$29.82	10.338%	$32.9028	$32.90	$32.90	$32.90
Purchase #6	$49.79	4.644%	$52.1022	$52.10	$52.10	$52.10
Purchase #7	$73.41	13.715%	$83.4782	$83.48	$83.50	$83.50
7 purchase totals =	$538.09		$585.2219	$585.22	$585.25	$585.20