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	$69.70	10.600%	$77.0882	$77.09	$77.10	$77.10
Purchase #2	$78.73	8.803%	$85.6606	$85.66	$85.65	$85.70
Purchase #3	$240.40	12.766%	$271.0895	$271.09	$271.10	$271.10
Purchase #4	$137.39	7.592%	$147.8206	$147.82	$147.80	$147.80
Purchase #5	$101.85	9.642%	$111.6704	$111.67	$111.65	$111.70
Purchase #6	$198.46	10.744%	$219.7825	$219.78	$219.80	$219.80
Purchase #7	$55.75	9.430%	$61.0072	$61.01	$61.00	$61.00
7 purchase totals =	$882.28		$974.1190	$974.12	$974.10	$974.20