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	$57.80	6.842%	$61.7547	$61.75	$61.75	$61.80
Purchase #2	$90.97	9.751%	$99.8405	$99.84	$99.85	$99.80
Purchase #3	$61.85	10.336%	$68.2428	$68.24	$68.25	$68.20
Purchase #4	$242.74	12.386%	$272.8058	$272.81	$272.80	$272.80
Purchase #5	$45.70	13.574%	$51.9033	$51.90	$51.90	$51.90
Purchase #6	$89.43	11.320%	$99.5535	$99.55	$99.55	$99.60
Purchase #7	$243.35	6.558%	$259.3089	$259.31	$259.30	$259.30
7 purchase totals =	$831.84		$913.4095	$913.40	$913.40	$913.40