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	$67.56	6.322%	$71.8311	$71.83	$71.85	$71.80
Purchase #2	$188.85	8.306%	$204.5359	$204.54	$204.55	$204.50
Purchase #3	$92.61	12.853%	$104.5132	$104.51	$104.50	$104.50
Purchase #4	$249.87	6.798%	$266.8562	$266.86	$266.85	$266.90
Purchase #5	$113.36	10.524%	$125.29	$125.29	$125.30	$125.30
Purchase #6	$85.66	5.563%	$90.4253	$90.43	$90.45	$90.40
Purchase #7	$96.84	8.640%	$105.207	$105.21	$105.20	$105.20
7 purchase totals =	$894.75		$968.6587	$968.67	$968.70	$968.60