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	$81.48	11.850%	$91.1354	$91.14	$91.15	$91.10
Purchase #2	$20.50	7.621%	$22.0623	$22.06	$22.05	$22.10
Purchase #3	$159.91	5.405%	$168.5531	$168.55	$168.55	$168.60
Purchase #4	$28.66	11.732%	$32.0224	$32.02	$32.00	$32.00
Purchase #5	$71.74	9.167%	$78.3164	$78.32	$78.30	$78.30
Purchase #6	$111.77	10.266%	$123.2443	$123.24	$123.25	$123.20
Purchase #7	$73.94	8.497%	$80.2227	$80.22	$80.20	$80.20
7 purchase totals =	$548.00		$595.5566	$595.55	$595.50	$595.50