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	$167.55	12.297%	$188.1536	$188.15	$188.15	$188.20
Purchase #2	$227.80	7.187%	$244.172	$244.17	$244.15	$244.20
Purchase #3	$29.50	12.334%	$33.1385	$33.14	$33.15	$33.10
Purchase #4	$221.77	8.466%	$240.545	$240.55	$240.55	$240.50
Purchase #5	$145.46	10.159%	$160.2373	$160.24	$160.25	$160.20
Purchase #6	$227.48	3.506%	$235.4554	$235.46	$235.45	$235.50
Purchase #7	$86.99	13.863%	$99.0494	$99.05	$99.05	$99.00
7 purchase totals =	$1,106.55		$1,200.7512	$1,200.76	$1,200.75	$1,200.70