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	$145.43	13.541%	$165.1227	$165.12	$165.10	$165.10
Purchase #2	$186.36	12.372%	$209.4165	$209.42	$209.40	$209.40
Purchase #3	$45.31	10.746%	$50.179	$50.18	$50.20	$50.20
Purchase #4	$120.72	5.228%	$127.0312	$127.03	$127.05	$127.00
Purchase #5	$71.80	13.408%	$81.4269	$81.43	$81.45	$81.40
Purchase #6	$129.72	5.825%	$137.2762	$137.28	$137.30	$137.30
Purchase #7	$191.57	7.524%	$205.9837	$205.98	$206.00	$206.00
7 purchase totals =	$890.91		$976.4362	$976.44	$976.50	$976.40