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	$104.59	12.365%	$117.5226	$117.52	$117.50	$117.50
Purchase #2	$196.74	9.666%	$215.7569	$215.76	$215.75	$215.80
Purchase #3	$37.50	12.585%	$42.2194	$42.22	$42.20	$42.20
Purchase #4	$205.78	4.146%	$214.3116	$214.31	$214.30	$214.30
Purchase #5	$72.46	11.576%	$80.848	$80.85	$80.85	$80.80
Purchase #6	$84.98	4.864%	$89.1134	$89.11	$89.10	$89.10
Purchase #7	$64.91	12.269%	$72.8738	$72.87	$72.85	$72.90
7 purchase totals =	$766.96		$832.6457	$832.64	$832.55	$832.60