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	$123.91	4.244%	$129.1687	$129.17	$129.15	$129.20
Purchase #2	$39.58	5.765%	$41.8618	$41.86	$41.85	$41.90
Purchase #3	$248.57	7.626%	$267.5259	$267.53	$267.55	$267.50
Purchase #4	$206.98	4.281%	$215.8408	$215.84	$215.85	$215.80
Purchase #5	$223.65	4.288%	$233.2401	$233.24	$233.25	$233.20
Purchase #6	$111.77	4.573%	$116.8812	$116.88	$116.90	$116.90
Purchase #7	$43.54	6.757%	$46.482	$46.48	$46.50	$46.50
7 purchase totals =	$998.00		$1,051.0005	$1,051.00	$1,051.05	$1,051.00