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	$39.56	7.578%	$42.5579	$42.56	$42.55	$42.60
Purchase #2	$155.48	10.294%	$171.4851	$171.49	$171.50	$171.50
Purchase #3	$17.36	7.412%	$18.6467	$18.65	$18.65	$18.60
Purchase #4	$173.97	5.741%	$183.9576	$183.96	$183.95	$184.00
Purchase #5	$200.30	12.289%	$224.9149	$224.91	$224.90	$224.90
Purchase #6	$243.44	8.392%	$263.8695	$263.87	$263.85	$263.90
Purchase #7	$185.43	4.562%	$193.8893	$193.89	$193.90	$193.90
7 purchase totals =	$1,015.54		$1,099.3210	$1,099.33	$1,099.30	$1,099.40