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	$104.58	4.531%	$109.3185	$109.32	$109.30	$109.30
Purchase #2	$30.83	6.212%	$32.7452	$32.75	$32.75	$32.70
Purchase #3	$150.29	13.818%	$171.0571	$171.06	$171.05	$171.10
Purchase #4	$140.73	3.797%	$146.0735	$146.07	$146.05	$146.10
Purchase #5	$30.63	12.812%	$34.5543	$34.55	$34.55	$34.60
Purchase #6	$45.48	13.342%	$51.5479	$51.55	$51.55	$51.50
Purchase #7	$71.79	10.154%	$79.0796	$79.08	$79.10	$79.10
7 purchase totals =	$574.33		$624.3761	$624.38	$624.35	$624.40