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	$92.46	6.359%	$98.3395	$98.34	$98.35	$98.30
Purchase #2	$52.84	11.348%	$58.8363	$58.84	$58.85	$58.80
Purchase #3	$46.72	6.720%	$49.8596	$49.86	$49.85	$49.90
Purchase #4	$85.59	4.156%	$89.1471	$89.15	$89.15	$89.10
Purchase #5	$249.46	6.283%	$265.1336	$265.13	$265.15	$265.10
Purchase #6	$195.48	13.185%	$221.254	$221.25	$221.25	$221.30
Purchase #7	$231.53	13.770%	$263.4117	$263.41	$263.40	$263.40
7 purchase totals =	$954.08		$1,045.9818	$1,045.98	$1,046.00	$1,045.90