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	$203.72	12.169%	$228.5107	$228.51	$228.50	$228.50
Purchase #2	$96.57	3.133%	$99.5955	$99.60	$99.60	$99.60
Purchase #3	$29.86	7.810%	$32.1921	$32.19	$32.20	$32.20
Purchase #4	$207.47	5.334%	$218.5364	$218.54	$218.55	$218.50
Purchase #5	$200.34	11.664%	$223.7077	$223.71	$223.70	$223.70
Purchase #6	$196.88	13.648%	$223.7502	$223.75	$223.75	$223.80
Purchase #7	$205.56	7.540%	$221.0592	$221.06	$221.05	$221.10
7 purchase totals =	$1,140.40		$1,247.3518	$1,247.36	$1,247.35	$1,247.40