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	$51.48	8.623%	$55.9191	$55.92	$55.90	$55.90
Purchase #2	$30.52	12.499%	$34.3347	$34.33	$34.35	$34.30
Purchase #3	$199.72	4.595%	$208.8971	$208.90	$208.90	$208.90
Purchase #4	$76.28	12.251%	$85.6251	$85.63	$85.65	$85.60
Purchase #5	$58.66	4.571%	$61.3413	$61.34	$61.35	$61.30
Purchase #6	$37.29	6.226%	$39.6117	$39.61	$39.60	$39.60
Purchase #7	$22.39	9.740%	$24.5708	$24.57	$24.55	$24.60
7 purchase totals =	$476.34		$510.2998	$510.30	$510.30	$510.20