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	$244.53	13.152%	$276.6906	$276.69	$276.70	$276.70
Purchase #2	$80.95	10.280%	$89.2717	$89.27	$89.25	$89.30
Purchase #3	$38.36	7.714%	$41.3191	$41.32	$41.30	$41.30
Purchase #4	$191.42	9.164%	$208.9617	$208.96	$208.95	$209.00
Purchase #5	$82.75	10.635%	$91.5505	$91.55	$91.55	$91.60
Purchase #6	$140.68	11.439%	$156.7724	$156.77	$156.75	$156.80
Purchase #7	$37.99	11.273%	$42.2726	$42.27	$42.25	$42.30
7 purchase totals =	$816.68		$906.8386	$906.83	$906.75	$907.00