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	$234.95	6.476%	$250.1654	$250.17	$250.15	$250.20
Purchase #2	$221.83	12.411%	$249.3613	$249.36	$249.35	$249.40
Purchase #3	$64.89	3.360%	$67.0703	$67.07	$67.05	$67.10
Purchase #4	$201.75	8.821%	$219.5464	$219.55	$219.55	$219.50
Purchase #5	$126.58	12.550%	$142.4658	$142.47	$142.45	$142.50
Purchase #6	$213.77	13.533%	$242.6995	$242.70	$242.70	$242.70
Purchase #7	$96.88	13.362%	$109.8251	$109.83	$109.85	$109.80
7 purchase totals =	$1,160.65		$1,281.1338	$1,281.15	$1,281.10	$1,281.20