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	$136.55	6.426%	$145.3247	$145.32	$145.30	$145.30
Purchase #2	$205.33	5.603%	$216.8346	$216.83	$216.85	$216.80
Purchase #3	$64.36	9.764%	$70.6441	$70.64	$70.65	$70.60
Purchase #4	$83.41	9.663%	$91.4699	$91.47	$91.45	$91.50
Purchase #5	$61.84	8.403%	$67.0364	$67.04	$67.05	$67.00
Purchase #6	$249.91	5.783%	$264.3623	$264.36	$264.35	$264.40
Purchase #7	$109.69	12.425%	$123.319	$123.32	$123.30	$123.30
7 purchase totals =	$911.09		$978.9910	$978.98	$978.95	$978.90