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	$159.56	8.167%	$172.5913	$172.59	$172.60	$172.60
Purchase #2	$65.78	8.214%	$71.1832	$71.18	$71.20	$71.20
Purchase #3	$245.88	9.228%	$268.5698	$268.57	$268.55	$268.60
Purchase #4	$109.46	7.401%	$117.5611	$117.56	$117.55	$117.60
Purchase #5	$250.27	10.347%	$276.1654	$276.17	$276.15	$276.20
Purchase #6	$173.80	4.485%	$181.5949	$181.59	$181.60	$181.60
Purchase #7	$30.98	9.380%	$33.8859	$33.89	$33.90	$33.90
7 purchase totals =	$1,035.73		$1,121.5516	$1,121.55	$1,121.55	$1,121.70