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	$155.59	10.261%	$171.5551	$171.56	$171.55	$171.60
Purchase #2	$64.77	11.734%	$72.3701	$72.37	$72.35	$72.40
Purchase #3	$124.60	4.298%	$129.9553	$129.96	$129.95	$130.00
Purchase #4	$90.73	7.214%	$97.2753	$97.28	$97.30	$97.30
Purchase #5	$85.34	6.736%	$91.0885	$91.09	$91.10	$91.10
Purchase #6	$201.45	8.235%	$218.0394	$218.04	$218.05	$218.00
Purchase #7	$250.69	11.488%	$279.4893	$279.49	$279.50	$279.50
7 purchase totals =	$973.17		$1,059.7730	$1,059.79	$1,059.80	$1,059.90