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	$171.68	10.165%	$189.1313	$189.13	$189.15	$189.10
Purchase #2	$89.57	11.216%	$99.6162	$99.62	$99.60	$99.60
Purchase #3	$151.50	6.190%	$160.8779	$160.88	$160.90	$160.90
Purchase #4	$172.26	4.799%	$180.5268	$180.53	$180.55	$180.50
Purchase #5	$14.56	4.811%	$15.2605	$15.26	$15.25	$15.30
Purchase #6	$72.70	10.427%	$80.2804	$80.28	$80.30	$80.30
Purchase #7	$24.37	11.530%	$27.1799	$27.18	$27.20	$27.20
7 purchase totals =	$696.64		$752.8730	$752.88	$752.95	$752.90