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	$228.87	7.389%	$245.7812	$245.78	$245.80	$245.80
Purchase #2	$71.87	9.364%	$78.5999	$78.60	$78.60	$78.60
Purchase #3	$140.46	4.582%	$146.8959	$146.90	$146.90	$146.90
Purchase #4	$96.37	11.537%	$107.4882	$107.49	$107.50	$107.50
Purchase #5	$18.75	8.435%	$20.3316	$20.33	$20.35	$20.30
Purchase #6	$135.26	11.339%	$150.5971	$150.60	$150.60	$150.60
Purchase #7	$99.36	9.228%	$108.5289	$108.53	$108.55	$108.50
7 purchase totals =	$790.94		$858.2228	$858.23	$858.30	$858.20