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	$154.32	13.475%	$175.1146	$175.11	$175.10	$175.10
Purchase #2	$61.25	7.476%	$65.8291	$65.83	$65.85	$65.80
Purchase #3	$162.34	12.816%	$183.1455	$183.15	$183.15	$183.10
Purchase #4	$136.62	6.349%	$145.294	$145.29	$145.30	$145.30
Purchase #5	$67.99	6.394%	$72.3373	$72.34	$72.35	$72.30
Purchase #6	$39.65	11.723%	$44.2982	$44.30	$44.30	$44.30
Purchase #7	$150.90	11.245%	$167.8687	$167.87	$167.85	$167.90
7 purchase totals =	$773.07		$853.8874	$853.89	$853.90	$853.80