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	$161.84	3.122%	$166.8926	$166.89	$166.90	$166.90
Purchase #2	$85.39	10.282%	$94.1698	$94.17	$94.15	$94.20
Purchase #3	$38.67	8.252%	$41.861	$41.86	$41.85	$41.90
Purchase #4	$36.29	6.564%	$38.6721	$38.67	$38.65	$38.70
Purchase #5	$59.29	13.584%	$67.344	$67.34	$67.35	$67.30
Purchase #6	$113.56	13.867%	$129.3074	$129.31	$129.30	$129.30
Purchase #7	$117.50	8.847%	$127.8952	$127.90	$127.90	$127.90
7 purchase totals =	$612.54		$666.1421	$666.14	$666.10	$666.20