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	$50.50	10.174%	$55.6379	$55.64	$55.65	$55.60
Purchase #2	$31.36	12.677%	$35.3355	$35.34	$35.35	$35.30
Purchase #3	$50.64	3.156%	$52.2382	$52.24	$52.25	$52.20
Purchase #4	$173.47	9.813%	$190.4926	$190.49	$190.50	$190.50
Purchase #5	$86.31	11.797%	$96.492	$96.49	$96.50	$96.50
Purchase #6	$189.89	13.701%	$215.9068	$215.91	$215.90	$215.90
Purchase #7	$57.58	6.300%	$61.2075	$61.21	$61.20	$61.20
7 purchase totals =	$639.75		$707.3105	$707.32	$707.35	$707.20