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	$39.87	5.806%	$42.1849	$42.18	$42.20	$42.20
Purchase #2	$213.54	13.872%	$243.1623	$243.16	$243.15	$243.20
Purchase #3	$72.25	5.360%	$76.1226	$76.12	$76.10	$76.10
Purchase #4	$19.36	5.253%	$20.377	$20.38	$20.40	$20.40
Purchase #5	$172.48	9.349%	$188.6052	$188.61	$188.60	$188.60
Purchase #6	$142.77	12.301%	$160.3321	$160.33	$160.35	$160.30
Purchase #7	$151.79	5.726%	$160.4815	$160.48	$160.50	$160.50
7 purchase totals =	$812.06		$891.2656	$891.26	$891.30	$891.30