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	$110.28	12.677%	$124.2602	$124.26	$124.25	$124.30
Purchase #2	$50.58	7.305%	$54.2749	$54.27	$54.25	$54.30
Purchase #3	$6.84	5.732%	$7.2321	$7.23	$7.25	$7.20
Purchase #4	$44.45	12.870%	$50.1707	$50.17	$50.15	$50.20
Purchase #5	$30.98	9.256%	$33.8475	$33.85	$33.85	$33.80
Purchase #6	$229.34	9.216%	$250.476	$250.48	$250.50	$250.50
Purchase #7	$73.69	10.597%	$81.4989	$81.50	$81.50	$81.50
7 purchase totals =	$546.16		$601.7603	$601.76	$601.75	$601.80