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	$33.51	13.151%	$37.9169	$37.92	$37.90	$37.90
Purchase #2	$128.82	13.264%	$145.9067	$145.91	$145.90	$145.90
Purchase #3	$99.87	10.458%	$110.3144	$110.31	$110.30	$110.30
Purchase #4	$65.89	12.120%	$73.8759	$73.88	$73.90	$73.90
Purchase #5	$249.58	5.821%	$264.1081	$264.11	$264.10	$264.10
Purchase #6	$44.99	12.338%	$50.5409	$50.54	$50.55	$50.50
Purchase #7	$79.41	3.280%	$82.0146	$82.01	$82.00	$82.00
7 purchase totals =	$702.07		$764.6775	$764.68	$764.65	$764.60