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	$223.57	12.263%	$250.9864	$250.99	$251.00	$251.00
Purchase #2	$105.61	3.243%	$109.0349	$109.03	$109.05	$109.00
Purchase #3	$93.85	4.234%	$97.8236	$97.82	$97.80	$97.80
Purchase #4	$98.29	3.638%	$101.8658	$101.87	$101.85	$101.90
Purchase #5	$128.30	11.342%	$142.8518	$142.85	$142.85	$142.90
Purchase #6	$98.89	10.765%	$109.5355	$109.54	$109.55	$109.50
Purchase #7	$105.38	9.192%	$115.0665	$115.07	$115.05	$115.10
7 purchase totals =	$853.89		$927.1645	$927.17	$927.15	$927.20