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	$73.99	8.864%	$80.5485	$80.55	$80.55	$80.50
Purchase #2	$205.54	11.466%	$229.1072	$229.11	$229.10	$229.10
Purchase #3	$170.49	4.695%	$178.4945	$178.49	$178.50	$178.50
Purchase #4	$243.60	12.788%	$274.7516	$274.75	$274.75	$274.80
Purchase #5	$47.43	12.329%	$53.2776	$53.28	$53.30	$53.30
Purchase #6	$225.96	5.124%	$237.5382	$237.54	$237.55	$237.50
Purchase #7	$85.54	4.353%	$89.2636	$89.26	$89.25	$89.30
7 purchase totals =	$1,052.55		$1,142.9812	$1,142.98	$1,143.00	$1,143.00