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	$130.45	6.190%	$138.5249	$138.52	$138.50	$138.50
Purchase #2	$84.34	7.710%	$90.8426	$90.84	$90.85	$90.80
Purchase #3	$139.35	13.625%	$158.3364	$158.34	$158.35	$158.30
Purchase #4	$162.85	13.689%	$185.1425	$185.14	$185.15	$185.10
Purchase #5	$30.27	3.817%	$31.4254	$31.43	$31.45	$31.40
Purchase #6	$64.87	12.251%	$72.8172	$72.82	$72.80	$72.80
Purchase #7	$146.25	8.184%	$158.2191	$158.22	$158.20	$158.20
7 purchase totals =	$758.38		$835.3081	$835.31	$835.30	$835.10