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	$62.57	13.262%	$70.868	$70.87	$70.85	$70.90
Purchase #2	$109.91	12.201%	$123.3201	$123.32	$123.30	$123.30
Purchase #3	$67.54	7.602%	$72.6744	$72.67	$72.65	$72.70
Purchase #4	$226.53	6.540%	$241.3451	$241.35	$241.35	$241.30
Purchase #5	$67.76	8.481%	$73.5067	$73.51	$73.50	$73.50
Purchase #6	$181.48	4.568%	$189.77	$189.77	$189.75	$189.80
Purchase #7	$121.55	7.173%	$130.2688	$130.27	$130.25	$130.30
7 purchase totals =	$837.34		$901.7531	$901.76	$901.65	$901.80