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	$59.56	12.727%	$67.1402	$67.14	$67.15	$67.10
Purchase #2	$77.30	3.800%	$80.2374	$80.24	$80.25	$80.20
Purchase #3	$140.57	10.489%	$155.3144	$155.31	$155.30	$155.30
Purchase #4	$18.30	4.317%	$19.09	$19.09	$19.10	$19.10
Purchase #5	$128.79	12.185%	$144.4831	$144.48	$144.50	$144.50
Purchase #6	$28.83	7.740%	$31.0614	$31.06	$31.05	$31.10
Purchase #7	$216.34	3.476%	$223.86	$223.86	$223.85	$223.90
7 purchase totals =	$669.69		$721.1865	$721.18	$721.20	$721.20