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	$135.49	4.740%	$141.9122	$141.91	$141.90	$141.90
Purchase #2	$41.26	3.209%	$42.584	$42.58	$42.60	$42.60
Purchase #3	$165.53	11.357%	$184.3292	$184.33	$184.35	$184.30
Purchase #4	$117.59	12.695%	$132.5181	$132.52	$132.50	$132.50
Purchase #5	$88.86	7.432%	$95.4641	$95.46	$95.45	$95.50
Purchase #6	$47.75	12.507%	$53.7221	$53.72	$53.70	$53.70
Purchase #7	$241.52	10.777%	$267.5486	$267.55	$267.55	$267.50
7 purchase totals =	$838.00		$918.0783	$918.07	$918.05	$918.00