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	$111.46	8.761%	$121.225	$121.23	$121.25	$121.20
Purchase #2	$135.33	11.655%	$151.1027	$151.10	$151.10	$151.10
Purchase #3	$231.46	12.608%	$260.6425	$260.64	$260.65	$260.60
Purchase #4	$134.28	13.535%	$152.4548	$152.45	$152.45	$152.50
Purchase #5	$87.42	13.731%	$99.4236	$99.42	$99.40	$99.40
Purchase #6	$150.34	8.339%	$162.8769	$162.88	$162.90	$162.90
Purchase #7	$245.80	13.121%	$278.0514	$278.05	$278.05	$278.10
7 purchase totals =	$1,096.09		$1,225.7769	$1,225.77	$1,225.80	$1,225.80