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	$153.52	13.375%	$174.0533	$174.05	$174.05	$174.10
Purchase #2	$20.29	4.215%	$21.1452	$21.15	$21.15	$21.10
Purchase #3	$85.32	12.636%	$96.101	$96.10	$96.10	$96.10
Purchase #4	$215.91	10.686%	$238.9821	$238.98	$239.00	$239.00
Purchase #5	$61.69	9.173%	$67.3488	$67.35	$67.35	$67.30
Purchase #6	$78.66	12.229%	$88.2793	$88.28	$88.30	$88.30
Purchase #7	$88.48	3.448%	$91.5308	$91.53	$91.55	$91.50
7 purchase totals =	$703.87		$777.4405	$777.44	$777.50	$777.40