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	$171.46	8.148%	$185.4306	$185.43	$185.45	$185.40
Purchase #2	$28.61	9.525%	$31.3351	$31.34	$31.35	$31.30
Purchase #3	$120.90	7.403%	$129.8502	$129.85	$129.85	$129.90
Purchase #4	$47.54	13.854%	$54.1262	$54.13	$54.15	$54.10
Purchase #5	$7.51	9.735%	$8.2411	$8.24	$8.25	$8.20
Purchase #6	$86.89	4.162%	$90.5064	$90.51	$90.50	$90.50
Purchase #7	$24.73	3.223%	$25.527	$25.53	$25.55	$25.50
7 purchase totals =	$487.64		$525.0166	$525.03	$525.10	$524.90