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	$248.60	6.401%	$264.5129	$264.51	$264.50	$264.50
Purchase #2	$185.69	6.293%	$197.3755	$197.38	$197.40	$197.40
Purchase #3	$34.36	7.269%	$36.8576	$36.86	$36.85	$36.90
Purchase #4	$86.65	6.568%	$92.3412	$92.34	$92.35	$92.30
Purchase #5	$145.88	7.298%	$156.5263	$156.53	$156.55	$156.50
Purchase #6	$66.56	9.132%	$72.6383	$72.64	$72.65	$72.60
Purchase #7	$165.60	8.687%	$179.9857	$179.99	$180.00	$180.00
7 purchase totals =	$933.34		$1,000.2375	$1,000.25	$1,000.30	$1,000.20