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	$82.59	7.118%	$88.4688	$88.47	$88.45	$88.50
Purchase #2	$43.92	10.448%	$48.5088	$48.51	$48.50	$48.50
Purchase #3	$157.83	12.220%	$177.1168	$177.12	$177.10	$177.10
Purchase #4	$19.54	10.229%	$21.5387	$21.54	$21.55	$21.50
Purchase #5	$103.82	6.362%	$110.425	$110.43	$110.45	$110.40
Purchase #6	$196.75	11.787%	$219.9409	$219.94	$219.95	$219.90
Purchase #7	$230.89	3.291%	$238.4886	$238.49	$238.50	$238.50
7 purchase totals =	$835.34		$904.4876	$904.50	$904.50	$904.40