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	$29.42	10.587%	$32.5347	$32.53	$32.55	$32.50
Purchase #2	$150.79	9.669%	$165.3699	$165.37	$165.35	$165.40
Purchase #3	$67.50	12.475%	$75.9206	$75.92	$75.90	$75.90
Purchase #4	$159.96	3.374%	$165.3571	$165.36	$165.35	$165.40
Purchase #5	$70.54	9.183%	$77.0177	$77.02	$77.00	$77.00
Purchase #6	$85.35	13.395%	$96.7826	$96.78	$96.80	$96.80
Purchase #7	$144.82	5.301%	$152.4969	$152.50	$152.50	$152.50
7 purchase totals =	$708.38		$765.4795	$765.48	$765.45	$765.50