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	$179.77	6.531%	$191.5108	$191.51	$191.50	$191.50
Purchase #2	$59.36	3.688%	$61.5492	$61.55	$61.55	$61.50
Purchase #3	$64.72	8.590%	$70.2794	$70.28	$70.30	$70.30
Purchase #4	$174.79	4.603%	$182.8356	$182.84	$182.85	$182.80
Purchase #5	$88.70	5.780%	$93.8269	$93.83	$93.85	$93.80
Purchase #6	$172.88	7.757%	$186.2903	$186.29	$186.30	$186.30
Purchase #7	$39.45	7.699%	$42.4873	$42.49	$42.50	$42.50
7 purchase totals =	$779.67		$828.7795	$828.79	$828.85	$828.70