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	$103.82	5.740%	$109.7793	$109.78	$109.80	$109.80
Purchase #2	$39.37	5.475%	$41.5255	$41.53	$41.55	$41.50
Purchase #3	$75.28	11.742%	$84.1194	$84.12	$84.10	$84.10
Purchase #4	$221.92	9.159%	$242.2457	$242.25	$242.25	$242.20
Purchase #5	$162.30	7.413%	$174.3313	$174.33	$174.35	$174.30
Purchase #6	$102.33	5.526%	$107.9848	$107.98	$108.00	$108.00
Purchase #7	$91.86	9.472%	$100.561	$100.56	$100.55	$100.60
7 purchase totals =	$796.88		$860.5470	$860.55	$860.60	$860.50