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	$150.36	3.662%	$155.8662	$155.87	$155.85	$155.90
Purchase #2	$200.27	6.429%	$213.1454	$213.15	$213.15	$213.10
Purchase #3	$36.42	13.339%	$41.2781	$41.28	$41.30	$41.30
Purchase #4	$140.33	13.631%	$159.4584	$159.46	$159.45	$159.50
Purchase #5	$141.45	7.701%	$152.3431	$152.34	$152.35	$152.30
Purchase #6	$91.70	5.155%	$96.4271	$96.43	$96.45	$96.40
Purchase #7	$131.77	11.575%	$147.0224	$147.02	$147.00	$147.00
7 purchase totals =	$892.30		$965.5407	$965.55	$965.55	$965.50