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	$129.94	7.208%	$139.3061	$139.31	$139.30	$139.30
Purchase #2	$122.36	8.633%	$132.9233	$132.92	$132.90	$132.90
Purchase #3	$176.49	12.211%	$198.0412	$198.04	$198.05	$198.00
Purchase #4	$125.56	12.587%	$141.3642	$141.36	$141.35	$141.40
Purchase #5	$72.30	7.198%	$77.5042	$77.50	$77.50	$77.50
Purchase #6	$56.82	8.722%	$61.7758	$61.78	$61.80	$61.80
Purchase #7	$250.84	9.356%	$274.3086	$274.31	$274.30	$274.30
7 purchase totals =	$934.31		$1,025.2234	$1,025.22	$1,025.20	$1,025.20