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	$229.46	5.617%	$242.3488	$242.35	$242.35	$242.30
Purchase #2	$80.75	10.587%	$89.299	$89.30	$89.30	$89.30
Purchase #3	$29.91	9.415%	$32.726	$32.73	$32.75	$32.70
Purchase #4	$148.99	12.791%	$168.0473	$168.05	$168.05	$168.00
Purchase #5	$98.52	12.841%	$111.171	$111.17	$111.15	$111.20
Purchase #6	$205.62	6.610%	$219.2115	$219.21	$219.20	$219.20
Purchase #7	$57.78	6.655%	$61.6253	$61.63	$61.65	$61.60
7 purchase totals =	$851.03		$924.4289	$924.44	$924.45	$924.30