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	$233.82	4.143%	$243.5072	$243.51	$243.50	$243.50
Purchase #2	$134.42	12.276%	$150.9214	$150.92	$150.90	$150.90
Purchase #3	$179.79	11.376%	$200.2429	$200.24	$200.25	$200.20
Purchase #4	$10.60	10.620%	$11.7257	$11.73	$11.75	$11.70
Purchase #5	$231.60	7.331%	$248.5786	$248.58	$248.60	$248.60
Purchase #6	$105.82	9.480%	$115.8517	$115.85	$115.85	$115.90
Purchase #7	$163.27	13.635%	$185.5319	$185.53	$185.55	$185.50
7 purchase totals =	$1,059.32		$1,156.3594	$1,156.36	$1,156.40	$1,156.30