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	$17.50	4.234%	$18.241	$18.24	$18.25	$18.20
Purchase #2	$108.55	5.145%	$114.1349	$114.13	$114.15	$114.10
Purchase #3	$189.56	12.736%	$213.7024	$213.70	$213.70	$213.70
Purchase #4	$83.53	6.705%	$89.1307	$89.13	$89.15	$89.10
Purchase #5	$98.59	11.700%	$110.125	$110.13	$110.15	$110.10
Purchase #6	$74.51	11.821%	$83.3178	$83.32	$83.30	$83.30
Purchase #7	$30.83	4.740%	$32.2913	$32.29	$32.30	$32.30
7 purchase totals =	$603.07		$660.9431	$660.94	$661.00	$660.80