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	$129.39	13.865%	$147.3299	$147.33	$147.35	$147.30
Purchase #2	$183.57	5.691%	$194.017	$194.02	$194.00	$194.00
Purchase #3	$216.54	12.165%	$242.8821	$242.88	$242.90	$242.90
Purchase #4	$56.36	10.485%	$62.2693	$62.27	$62.25	$62.30
Purchase #5	$216.71	6.511%	$230.82	$230.82	$230.80	$230.80
Purchase #6	$119.29	4.607%	$124.7857	$124.79	$124.80	$124.80
Purchase #7	$75.29	4.676%	$78.8106	$78.81	$78.80	$78.80
7 purchase totals =	$997.15		$1,080.9146	$1,080.92	$1,080.90	$1,080.90