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	$97.47	3.311%	$100.6972	$100.70	$100.70	$100.70
Purchase #2	$141.80	7.543%	$152.496	$152.50	$152.50	$152.50
Purchase #3	$65.98	10.686%	$73.0306	$73.03	$73.05	$73.00
Purchase #4	$200.34	10.446%	$221.2675	$221.27	$221.25	$221.30
Purchase #5	$125.56	11.206%	$139.6303	$139.63	$139.65	$139.60
Purchase #6	$37.35	11.839%	$41.7719	$41.77	$41.75	$41.80
Purchase #7	$111.48	3.498%	$115.3796	$115.38	$115.40	$115.40
7 purchase totals =	$779.98		$844.2731	$844.28	$844.30	$844.30