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	$103.93	10.770%	$115.1233	$115.12	$115.10	$115.10
Purchase #2	$89.34	9.806%	$98.1007	$98.10	$98.10	$98.10
Purchase #3	$175.95	11.461%	$196.1156	$196.12	$196.10	$196.10
Purchase #4	$6.64	10.761%	$7.3545	$7.35	$7.35	$7.40
Purchase #5	$30.68	7.258%	$32.9068	$32.91	$32.90	$32.90
Purchase #6	$157.38	10.571%	$174.0166	$174.02	$174.00	$174.00
Purchase #7	$129.39	9.186%	$141.2758	$141.28	$141.30	$141.30
7 purchase totals =	$693.31		$764.8933	$764.90	$764.85	$764.90