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	$96.61	6.506%	$102.8954	$102.90	$102.90	$102.90
Purchase #2	$89.81	11.179%	$99.8499	$99.85	$99.85	$99.80
Purchase #3	$229.94	9.752%	$252.3637	$252.36	$252.35	$252.40
Purchase #4	$173.68	3.336%	$179.474	$179.47	$179.45	$179.50
Purchase #5	$37.71	4.830%	$39.5314	$39.53	$39.55	$39.50
Purchase #6	$28.94	11.582%	$32.2918	$32.29	$32.30	$32.30
Purchase #7	$200.36	5.756%	$211.8927	$211.89	$211.90	$211.90
7 purchase totals =	$857.05		$918.2989	$918.29	$918.30	$918.30