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	$29.34	12.583%	$33.0319	$33.03	$33.05	$33.00
Purchase #2	$178.91	9.703%	$196.2696	$196.27	$196.25	$196.30
Purchase #3	$85.96	8.582%	$93.3371	$93.34	$93.35	$93.30
Purchase #4	$70.28	9.712%	$77.1056	$77.11	$77.10	$77.10
Purchase #5	$174.29	8.206%	$188.5922	$188.59	$188.60	$188.60
Purchase #6	$234.67	6.729%	$250.4609	$250.46	$250.45	$250.50
Purchase #7	$148.77	5.830%	$157.4433	$157.44	$157.45	$157.40
7 purchase totals =	$922.22		$996.2406	$996.24	$996.25	$996.20