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	$226.27	12.742%	$255.1013	$255.10	$255.10	$255.10
Purchase #2	$162.50	13.404%	$184.2815	$184.28	$184.30	$184.30
Purchase #3	$124.25	9.267%	$135.7642	$135.76	$135.75	$135.80
Purchase #4	$126.74	11.309%	$141.073	$141.07	$141.05	$141.10
Purchase #5	$181.57	8.238%	$196.5277	$196.53	$196.55	$196.50
Purchase #6	$115.27	11.767%	$128.8338	$128.83	$128.85	$128.80
Purchase #7	$169.93	11.705%	$189.8203	$189.82	$189.80	$189.80
7 purchase totals =	$1,106.53		$1,231.4018	$1,231.39	$1,231.40	$1,231.40