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	$184.94	10.564%	$204.4771	$204.48	$204.50	$204.50
Purchase #2	$61.86	8.529%	$67.136	$67.14	$67.15	$67.10
Purchase #3	$27.76	13.384%	$31.4754	$31.48	$31.50	$31.50
Purchase #4	$173.75	3.736%	$180.2413	$180.24	$180.25	$180.20
Purchase #5	$41.34	5.460%	$43.5972	$43.60	$43.60	$43.60
Purchase #6	$17.69	3.328%	$18.2787	$18.28	$18.30	$18.30
Purchase #7	$47.98	5.349%	$50.5465	$50.55	$50.55	$50.50
7 purchase totals =	$555.32		$595.7522	$595.77	$595.85	$595.70