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	$120.37	6.129%	$127.7475	$127.75	$127.75	$127.70
Purchase #2	$84.54	7.858%	$91.1832	$91.18	$91.20	$91.20
Purchase #3	$218.48	12.516%	$245.825	$245.83	$245.85	$245.80
Purchase #4	$227.69	10.177%	$250.862	$250.86	$250.85	$250.90
Purchase #5	$156.33	6.582%	$166.6196	$166.62	$166.60	$166.60
Purchase #6	$158.71	13.626%	$180.3358	$180.34	$180.35	$180.30
Purchase #7	$166.68	3.524%	$172.5538	$172.55	$172.55	$172.60
7 purchase totals =	$1,132.80		$1,235.1269	$1,235.13	$1,235.15	$1,235.10