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	$125.41	10.353%	$138.3937	$138.39	$138.40	$138.40
Purchase #2	$72.40	11.108%	$80.4422	$80.44	$80.45	$80.40
Purchase #3	$198.55	9.738%	$217.8848	$217.88	$217.90	$217.90
Purchase #4	$78.26	13.116%	$88.5246	$88.52	$88.50	$88.50
Purchase #5	$180.52	7.234%	$193.5788	$193.58	$193.60	$193.60
Purchase #6	$140.75	7.281%	$150.998	$151.00	$151.00	$151.00
Purchase #7	$174.26	9.870%	$191.4595	$191.46	$191.45	$191.50
7 purchase totals =	$970.15		$1,061.2816	$1,061.27	$1,061.30	$1,061.30