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	$86.84	3.437%	$89.8247	$89.82	$89.80	$89.80
Purchase #2	$160.35	3.724%	$166.3214	$166.32	$166.30	$166.30
Purchase #3	$245.38	12.237%	$275.4072	$275.41	$275.40	$275.40
Purchase #4	$201.27	13.246%	$227.9302	$227.93	$227.95	$227.90
Purchase #5	$47.40	10.793%	$52.5159	$52.52	$52.50	$52.50
Purchase #6	$98.46	11.802%	$110.0802	$110.08	$110.10	$110.10
Purchase #7	$19.34	3.510%	$20.0188	$20.02	$20.00	$20.00
7 purchase totals =	$859.04		$942.0984	$942.10	$942.05	$942.00