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	$241.92	3.367%	$250.0654	$250.07	$250.05	$250.10
Purchase #2	$217.82	4.259%	$227.097	$227.10	$227.10	$227.10
Purchase #3	$142.30	3.408%	$147.1496	$147.15	$147.15	$147.10
Purchase #4	$169.39	6.546%	$180.4783	$180.48	$180.50	$180.50
Purchase #5	$13.49	13.866%	$15.3605	$15.36	$15.35	$15.40
Purchase #6	$177.39	12.134%	$198.9145	$198.91	$198.90	$198.90
Purchase #7	$119.57	9.607%	$131.0571	$131.06	$131.05	$131.10
7 purchase totals =	$1,081.88		$1,150.1224	$1,150.13	$1,150.10	$1,150.20