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	$76.71	5.757%	$81.1262	$81.13	$81.15	$81.10
Purchase #2	$162.27	3.505%	$167.9576	$167.96	$167.95	$168.00
Purchase #3	$172.51	8.592%	$187.3321	$187.33	$187.35	$187.30
Purchase #4	$109.34	10.199%	$120.4916	$120.49	$120.50	$120.50
Purchase #5	$46.63	10.475%	$51.5145	$51.51	$51.50	$51.50
Purchase #6	$169.33	7.168%	$181.4676	$181.47	$181.45	$181.50
Purchase #7	$51.65	7.648%	$55.6002	$55.60	$55.60	$55.60
7 purchase totals =	$788.44		$845.4898	$845.49	$845.50	$845.50