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	$29.70	7.250%	$31.8533	$31.85	$31.85	$31.90
Purchase #2	$81.91	5.262%	$86.2201	$86.22	$86.20	$86.20
Purchase #3	$243.61	4.221%	$253.8928	$253.89	$253.90	$253.90
Purchase #4	$157.87	13.693%	$179.4871	$179.49	$179.50	$179.50
Purchase #5	$191.45	6.674%	$204.2274	$204.23	$204.25	$204.20
Purchase #6	$236.77	10.422%	$261.4462	$261.45	$261.45	$261.40
Purchase #7	$39.51	4.771%	$41.395	$41.40	$41.40	$41.40
7 purchase totals =	$980.82		$1,058.5219	$1,058.53	$1,058.55	$1,058.50