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	$138.77	6.211%	$147.389	$147.39	$147.40	$147.40
Purchase #2	$210.41	6.322%	$223.7121	$223.71	$223.70	$223.70
Purchase #3	$216.63	11.655%	$241.8782	$241.88	$241.90	$241.90
Purchase #4	$172.33	12.526%	$193.9161	$193.92	$193.90	$193.90
Purchase #5	$27.97	12.568%	$31.4853	$31.49	$31.50	$31.50
Purchase #6	$41.60	3.648%	$43.1176	$43.12	$43.10	$43.10
Purchase #7	$128.64	5.785%	$136.0818	$136.08	$136.10	$136.10
7 purchase totals =	$936.35		$1,017.5801	$1,017.59	$1,017.60	$1,017.60