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	$31.59	7.271%	$33.8869	$33.89	$33.90	$33.90
Purchase #2	$83.62	9.758%	$91.7796	$91.78	$91.80	$91.80
Purchase #3	$48.25	12.830%	$54.4405	$54.44	$54.45	$54.40
Purchase #4	$127.74	7.520%	$137.346	$137.35	$137.35	$137.30
Purchase #5	$228.43	4.614%	$238.9698	$238.97	$238.95	$239.00
Purchase #6	$215.82	13.472%	$244.8953	$244.90	$244.90	$244.90
Purchase #7	$49.41	6.524%	$52.6335	$52.63	$52.65	$52.60
7 purchase totals =	$784.86		$853.9516	$853.96	$854.00	$853.90