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	$185.90	10.162%	$204.7912	$204.79	$204.80	$204.80
Purchase #2	$94.34	9.486%	$103.2891	$103.29	$103.30	$103.30
Purchase #3	$112.27	10.384%	$123.9281	$123.93	$123.95	$123.90
Purchase #4	$190.31	11.299%	$211.8131	$211.81	$211.80	$211.80
Purchase #5	$216.55	12.415%	$243.4347	$243.43	$243.45	$243.40
Purchase #6	$173.63	12.870%	$195.9762	$195.98	$196.00	$196.00
Purchase #7	$101.79	4.215%	$106.0804	$106.08	$106.10	$106.10
7 purchase totals =	$1,074.79		$1,189.3128	$1,189.31	$1,189.40	$1,189.30