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	$123.93	13.139%	$140.2132	$140.21	$140.20	$140.20
Purchase #2	$31.46	5.766%	$33.274	$33.27	$33.25	$33.30
Purchase #3	$119.35	6.866%	$127.5446	$127.54	$127.55	$127.50
Purchase #4	$67.36	4.670%	$70.5057	$70.51	$70.50	$70.50
Purchase #5	$145.33	10.663%	$160.8265	$160.83	$160.85	$160.80
Purchase #6	$88.72	12.697%	$99.9848	$99.98	$100.00	$100.00
Purchase #7	$170.91	6.463%	$181.9559	$181.96	$181.95	$182.00
7 purchase totals =	$747.06		$814.3047	$814.30	$814.30	$814.30