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	$242.85	12.867%	$274.0975	$274.10	$274.10	$274.10
Purchase #2	$37.63	7.473%	$40.4421	$40.44	$40.45	$40.40
Purchase #3	$79.56	12.805%	$89.7477	$89.75	$89.75	$89.70
Purchase #4	$40.27	12.797%	$45.4234	$45.42	$45.40	$45.40
Purchase #5	$181.89	6.252%	$193.2618	$193.26	$193.25	$193.30
Purchase #6	$182.47	9.813%	$200.3758	$200.38	$200.40	$200.40
Purchase #7	$219.48	10.581%	$242.7032	$242.70	$242.70	$242.70
7 purchase totals =	$984.15		$1,086.0515	$1,086.05	$1,086.05	$1,086.00