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	$35.77	3.776%	$37.1207	$37.12	$37.10	$37.10
Purchase #2	$127.28	5.136%	$133.8171	$133.82	$133.80	$133.80
Purchase #3	$87.48	4.351%	$91.2863	$91.29	$91.30	$91.30
Purchase #4	$154.53	9.680%	$169.4885	$169.49	$169.50	$169.50
Purchase #5	$128.42	10.871%	$142.3805	$142.38	$142.40	$142.40
Purchase #6	$27.96	13.763%	$31.8081	$31.81	$31.80	$31.80
Purchase #7	$166.76	12.415%	$187.4633	$187.46	$187.45	$187.50
7 purchase totals =	$728.20		$793.3645	$793.37	$793.35	$793.40