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	$245.27	13.161%	$277.55	$277.55	$277.55	$277.60
Purchase #2	$150.61	7.115%	$161.3259	$161.33	$161.35	$161.30
Purchase #3	$63.76	6.238%	$67.7373	$67.74	$67.75	$67.70
Purchase #4	$117.47	9.242%	$128.3266	$128.33	$128.35	$128.30
Purchase #5	$229.29	12.657%	$258.3112	$258.31	$258.30	$258.30
Purchase #6	$38.58	9.317%	$42.1745	$42.17	$42.15	$42.20
Purchase #7	$57.30	13.240%	$64.8865	$64.89	$64.90	$64.90
7 purchase totals =	$902.28		$1,000.3120	$1,000.32	$1,000.35	$1,000.30