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	$49.94	10.814%	$55.3405	$55.34	$55.35	$55.30
Purchase #2	$188.98	10.250%	$208.3505	$208.35	$208.35	$208.40
Purchase #3	$167.69	10.669%	$185.5808	$185.58	$185.60	$185.60
Purchase #4	$209.91	9.253%	$229.333	$229.33	$229.35	$229.30
Purchase #5	$16.29	4.584%	$17.0367	$17.04	$17.05	$17.00
Purchase #6	$42.45	7.740%	$45.7356	$45.74	$45.75	$45.70
Purchase #7	$92.37	6.153%	$98.0535	$98.05	$98.05	$98.10
7 purchase totals =	$767.63		$839.4306	$839.43	$839.50	$839.40