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	$239.72	4.611%	$250.7735	$250.77	$250.75	$250.80
Purchase #2	$187.34	4.742%	$196.2237	$196.22	$196.20	$196.20
Purchase #3	$230.74	9.790%	$253.3294	$253.33	$253.35	$253.30
Purchase #4	$93.57	5.325%	$98.5526	$98.55	$98.55	$98.60
Purchase #5	$158.36	7.491%	$170.2227	$170.22	$170.20	$170.20
Purchase #6	$20.84	3.389%	$21.5463	$21.55	$21.55	$21.50
Purchase #7	$37.71	11.379%	$42.001	$42.00	$42.00	$42.00
7 purchase totals =	$968.28		$1,032.6492	$1,032.64	$1,032.60	$1,032.60