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	$78.41	6.796%	$83.7387	$83.74	$83.75	$83.70
Purchase #2	$157.54	5.234%	$165.7856	$165.79	$165.80	$165.80
Purchase #3	$141.35	3.124%	$145.7658	$145.77	$145.75	$145.80
Purchase #4	$180.88	5.465%	$190.7651	$190.77	$190.75	$190.80
Purchase #5	$182.50	4.316%	$190.3767	$190.38	$190.40	$190.40
Purchase #6	$168.70	7.453%	$181.2732	$181.27	$181.25	$181.30
Purchase #7	$21.73	12.404%	$24.4254	$24.43	$24.45	$24.40
7 purchase totals =	$931.11		$982.1305	$982.15	$982.15	$982.20