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	$12.36	4.330%	$12.8952	$12.90	$12.90	$12.90
Purchase #2	$109.43	4.775%	$114.6553	$114.66	$114.65	$114.70
Purchase #3	$5.34	5.367%	$5.6266	$5.63	$5.65	$5.60
Purchase #4	$151.32	6.511%	$161.1724	$161.17	$161.15	$161.20
Purchase #5	$72.99	13.558%	$82.886	$82.89	$82.90	$82.90
Purchase #6	$36.40	3.145%	$37.5448	$37.54	$37.55	$37.50
Purchase #7	$146.47	6.597%	$156.1326	$156.13	$156.15	$156.10
7 purchase totals =	$534.31		$570.9129	$570.92	$570.95	$570.90