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	$30.62	8.282%	$33.1559	$33.16	$33.15	$33.20
Purchase #2	$222.72	12.501%	$250.5622	$250.56	$250.55	$250.60
Purchase #3	$214.54	13.224%	$242.9108	$242.91	$242.90	$242.90
Purchase #4	$246.58	8.423%	$267.3494	$267.35	$267.35	$267.30
Purchase #5	$38.26	9.836%	$42.0233	$42.02	$42.00	$42.00
Purchase #6	$73.90	11.600%	$82.4724	$82.47	$82.45	$82.50
Purchase #7	$68.47	4.126%	$71.2951	$71.30	$71.30	$71.30
7 purchase totals =	$895.09		$989.7691	$989.77	$989.70	$989.80