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	$69.96	12.761%	$78.8876	$78.89	$78.90	$78.90
Purchase #2	$240.26	6.789%	$256.5713	$256.57	$256.55	$256.60
Purchase #3	$239.77	10.819%	$265.7107	$265.71	$265.70	$265.70
Purchase #4	$107.25	3.645%	$111.1593	$111.16	$111.15	$111.20
Purchase #5	$112.51	6.689%	$120.0358	$120.04	$120.05	$120.00
Purchase #6	$162.72	5.688%	$171.9755	$171.98	$172.00	$172.00
Purchase #7	$72.97	8.788%	$79.3826	$79.38	$79.40	$79.40
7 purchase totals =	$1,005.44		$1,083.7228	$1,083.73	$1,083.75	$1,083.80