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	$86.70	3.150%	$89.4311	$89.43	$89.45	$89.40
Purchase #2	$47.80	7.872%	$51.5628	$51.56	$51.55	$51.60
Purchase #3	$91.60	8.402%	$99.2962	$99.30	$99.30	$99.30
Purchase #4	$29.37	7.448%	$31.5575	$31.56	$31.55	$31.60
Purchase #5	$47.29	13.351%	$53.6037	$53.60	$53.60	$53.60
Purchase #6	$245.32	4.313%	$255.9007	$255.90	$255.90	$255.90
Purchase #7	$59.56	3.649%	$61.7333	$61.73	$61.75	$61.70
7 purchase totals =	$607.64		$643.0853	$643.08	$643.10	$643.10