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	$42.25	9.783%	$46.3833	$46.38	$46.40	$46.40
Purchase #2	$16.37	10.351%	$18.0645	$18.06	$18.05	$18.10
Purchase #3	$154.51	11.202%	$171.8182	$171.82	$171.80	$171.80
Purchase #4	$84.78	13.489%	$96.216	$96.22	$96.20	$96.20
Purchase #5	$134.87	5.776%	$142.6601	$142.66	$142.65	$142.70
Purchase #6	$79.73	3.514%	$82.5317	$82.53	$82.55	$82.50
Purchase #7	$67.90	7.197%	$72.7868	$72.79	$72.80	$72.80
7 purchase totals =	$580.41		$630.4606	$630.46	$630.45	$630.50