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	$248.31	13.762%	$282.4824	$282.48	$282.50	$282.50
Purchase #2	$134.48	5.260%	$141.5536	$141.55	$141.55	$141.60
Purchase #3	$69.86	9.128%	$76.2368	$76.24	$76.25	$76.20
Purchase #4	$211.71	5.362%	$223.0619	$223.06	$223.05	$223.10
Purchase #5	$155.28	12.227%	$174.2661	$174.27	$174.25	$174.30
Purchase #6	$79.48	8.732%	$86.4202	$86.42	$86.40	$86.40
Purchase #7	$89.67	10.620%	$99.193	$99.19	$99.20	$99.20
7 purchase totals =	$988.79		$1,083.2140	$1,083.21	$1,083.20	$1,083.30