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	$198.47	5.558%	$209.501	$209.50	$209.50	$209.50
Purchase #2	$144.71	3.244%	$149.4044	$149.40	$149.40	$149.40
Purchase #3	$90.83	12.675%	$102.3427	$102.34	$102.35	$102.30
Purchase #4	$165.30	8.290%	$179.0034	$179.00	$179.00	$179.00
Purchase #5	$18.25	3.461%	$18.8816	$18.88	$18.90	$18.90
Purchase #6	$189.56	9.851%	$208.2336	$208.23	$208.25	$208.20
Purchase #7	$124.28	9.563%	$136.1649	$136.16	$136.15	$136.20
7 purchase totals =	$931.40		$1,003.5316	$1,003.51	$1,003.55	$1,003.50