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	$123.66	10.423%	$136.5491	$136.55	$136.55	$136.50
Purchase #2	$243.87	11.270%	$271.3541	$271.35	$271.35	$271.40
Purchase #3	$236.56	9.497%	$259.0261	$259.03	$259.05	$259.00
Purchase #4	$76.61	7.194%	$82.1213	$82.12	$82.10	$82.10
Purchase #5	$78.34	9.692%	$85.9327	$85.93	$85.95	$85.90
Purchase #6	$91.77	8.593%	$99.6558	$99.66	$99.65	$99.70
Purchase #7	$82.60	4.232%	$86.0956	$86.10	$86.10	$86.10
7 purchase totals =	$933.41		$1,020.7347	$1,020.74	$1,020.75	$1,020.70