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	$40.63	3.712%	$42.1382	$42.14	$42.15	$42.10
Purchase #2	$25.86	11.815%	$28.9154	$28.92	$28.90	$28.90
Purchase #3	$18.64	5.343%	$19.6359	$19.64	$19.65	$19.60
Purchase #4	$51.33	12.442%	$57.7165	$57.72	$57.70	$57.70
Purchase #5	$14.95	3.686%	$15.5011	$15.50	$15.50	$15.50
Purchase #6	$48.56	11.425%	$54.108	$54.11	$54.10	$54.10
Purchase #7	$34.84	8.524%	$37.8098	$37.81	$37.80	$37.80
7 purchase totals =	$234.81		$255.8249	$255.84	$255.80	$255.70