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	$89.88	12.172%	$100.8202	$100.82	$100.80	$100.80
Purchase #2	$176.55	7.355%	$189.5353	$189.54	$189.55	$189.50
Purchase #3	$46.66	7.642%	$50.2258	$50.23	$50.25	$50.20
Purchase #4	$174.76	11.130%	$194.2108	$194.21	$194.20	$194.20
Purchase #5	$49.60	10.795%	$54.9543	$54.95	$54.95	$55.00
Purchase #6	$112.90	4.481%	$117.959	$117.96	$117.95	$118.00
Purchase #7	$245.63	10.150%	$270.5614	$270.56	$270.55	$270.60
7 purchase totals =	$895.98		$978.2668	$978.27	$978.25	$978.30