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	$82.33	8.130%	$89.0234	$89.02	$89.00	$89.00
Purchase #2	$24.53	3.231%	$25.3226	$25.32	$25.30	$25.30
Purchase #3	$237.33	6.108%	$251.8261	$251.83	$251.85	$251.80
Purchase #4	$243.33	10.456%	$268.7726	$268.77	$268.75	$268.80
Purchase #5	$37.54	6.658%	$40.0394	$40.04	$40.05	$40.00
Purchase #6	$126.81	7.214%	$135.9581	$135.96	$135.95	$136.00
Purchase #7	$70.27	11.297%	$78.2084	$78.21	$78.20	$78.20
7 purchase totals =	$822.14		$889.1506	$889.15	$889.10	$889.10