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	$184.42	10.369%	$203.5425	$203.54	$203.55	$203.50
Purchase #2	$54.30	10.173%	$59.8239	$59.82	$59.80	$59.80
Purchase #3	$118.43	9.353%	$129.5068	$129.51	$129.50	$129.50
Purchase #4	$85.92	5.259%	$90.4385	$90.44	$90.45	$90.40
Purchase #5	$220.64	3.263%	$227.8395	$227.84	$227.85	$227.80
Purchase #6	$30.89	9.397%	$33.7927	$33.79	$33.80	$33.80
Purchase #7	$165.83	12.163%	$185.9999	$186.00	$186.00	$186.00
7 purchase totals =	$860.43		$930.9438	$930.94	$930.95	$930.80