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	$6.83	4.638%	$7.1468	$7.15	$7.15	$7.10
Purchase #2	$152.47	11.323%	$169.7342	$169.73	$169.75	$169.70
Purchase #3	$42.41	7.109%	$45.4249	$45.42	$45.40	$45.40
Purchase #4	$72.56	11.784%	$81.1105	$81.11	$81.10	$81.10
Purchase #5	$118.73	10.735%	$131.4757	$131.48	$131.50	$131.50
Purchase #6	$212.84	10.830%	$235.8906	$235.89	$235.90	$235.90
Purchase #7	$26.54	10.808%	$29.4084	$29.41	$29.40	$29.40
7 purchase totals =	$632.38		$700.1911	$700.19	$700.20	$700.10