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	$225.54	12.460%	$253.6423	$253.64	$253.65	$253.60
Purchase #2	$89.85	10.680%	$99.446	$99.45	$99.45	$99.40
Purchase #3	$188.46	4.523%	$196.984	$196.98	$197.00	$197.00
Purchase #4	$57.49	6.790%	$61.3936	$61.39	$61.40	$61.40
Purchase #5	$6.84	7.446%	$7.3493	$7.35	$7.35	$7.30
Purchase #6	$159.59	11.767%	$178.369	$178.37	$178.35	$178.40
Purchase #7	$77.63	7.794%	$83.6805	$83.68	$83.70	$83.70
7 purchase totals =	$805.40		$880.8647	$880.86	$880.90	$880.80