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	$147.73	11.594%	$164.8578	$164.86	$164.85	$164.90
Purchase #2	$25.50	8.735%	$27.7274	$27.73	$27.75	$27.70
Purchase #3	$81.29	9.566%	$89.0662	$89.07	$89.05	$89.10
Purchase #4	$73.93	9.240%	$80.7611	$80.76	$80.75	$80.80
Purchase #5	$29.61	13.474%	$33.5997	$33.60	$33.60	$33.60
Purchase #6	$92.54	7.200%	$99.2029	$99.20	$99.20	$99.20
Purchase #7	$243.32	11.536%	$271.3894	$271.39	$271.40	$271.40
7 purchase totals =	$693.92		$766.6045	$766.61	$766.60	$766.70