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	$134.69	8.600%	$146.2733	$146.27	$146.25	$146.30
Purchase #2	$106.53	9.753%	$116.9199	$116.92	$116.90	$116.90
Purchase #3	$175.82	7.345%	$188.734	$188.73	$188.75	$188.70
Purchase #4	$67.36	7.740%	$72.5737	$72.57	$72.55	$72.60
Purchase #5	$72.71	11.465%	$81.0462	$81.05	$81.05	$81.00
Purchase #6	$183.25	7.110%	$196.2791	$196.28	$196.30	$196.30
Purchase #7	$43.65	12.768%	$49.2232	$49.22	$49.20	$49.20
7 purchase totals =	$784.01		$851.0494	$851.04	$851.00	$851.00