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	$82.40	10.319%	$90.9029	$90.90	$90.90	$90.90
Purchase #2	$235.32	12.252%	$264.1514	$264.15	$264.15	$264.20
Purchase #3	$106.78	7.806%	$115.1152	$115.12	$115.10	$115.10
Purchase #4	$53.55	9.679%	$58.7331	$58.73	$58.75	$58.70
Purchase #5	$132.54	5.268%	$139.5222	$139.52	$139.50	$139.50
Purchase #6	$102.65	6.336%	$109.1539	$109.15	$109.15	$109.20
Purchase #7	$162.86	3.437%	$168.4575	$168.46	$168.45	$168.50
7 purchase totals =	$876.10		$946.0362	$946.03	$946.00	$946.10