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	$10.32	9.627%	$11.3135	$11.31	$11.30	$11.30
Purchase #2	$37.51	10.648%	$41.5041	$41.50	$41.50	$41.50
Purchase #3	$16.51	4.872%	$17.3144	$17.31	$17.30	$17.30
Purchase #4	$179.61	5.134%	$188.8312	$188.83	$188.85	$188.80
Purchase #5	$80.81	12.133%	$90.6147	$90.61	$90.60	$90.60
Purchase #6	$161.53	3.432%	$167.0737	$167.07	$167.05	$167.10
Purchase #7	$64.51	10.817%	$71.488	$71.49	$71.50	$71.50
7 purchase totals =	$550.80		$588.1396	$588.12	$588.10	$588.10