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	$245.95	9.499%	$269.3128	$269.31	$269.30	$269.30
Purchase #2	$144.53	13.737%	$164.3841	$164.38	$164.40	$164.40
Purchase #3	$83.64	9.418%	$91.5172	$91.52	$91.50	$91.50
Purchase #4	$137.98	6.152%	$146.4685	$146.47	$146.45	$146.50
Purchase #5	$31.80	12.189%	$35.6761	$35.68	$35.70	$35.70
Purchase #6	$130.35	7.522%	$140.1549	$140.15	$140.15	$140.20
Purchase #7	$41.47	8.560%	$45.0198	$45.02	$45.00	$45.00
7 purchase totals =	$815.72		$892.5334	$892.53	$892.50	$892.60