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	$205.91	4.498%	$215.1718	$215.17	$215.15	$215.20
Purchase #2	$249.98	5.796%	$264.4688	$264.47	$264.45	$264.50
Purchase #3	$177.51	10.532%	$196.2054	$196.21	$196.20	$196.20
Purchase #4	$231.42	5.822%	$244.8933	$244.89	$244.90	$244.90
Purchase #5	$77.35	6.664%	$82.5046	$82.50	$82.50	$82.50
Purchase #6	$207.83	7.196%	$222.7854	$222.79	$222.80	$222.80
Purchase #7	$100.42	13.739%	$114.2167	$114.22	$114.20	$114.20
7 purchase totals =	$1,250.42		$1,340.2460	$1,340.25	$1,340.20	$1,340.30