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	$165.94	7.569%	$178.5	$178.50	$178.50	$178.50
Purchase #2	$64.54	12.263%	$72.4545	$72.45	$72.45	$72.50
Purchase #3	$181.70	3.609%	$188.2576	$188.26	$188.25	$188.30
Purchase #4	$64.75	10.779%	$71.7294	$71.73	$71.75	$71.70
Purchase #5	$60.65	4.248%	$63.2264	$63.23	$63.25	$63.20
Purchase #6	$42.67	6.641%	$45.5037	$45.50	$45.50	$45.50
Purchase #7	$201.34	9.145%	$219.7525	$219.75	$219.75	$219.80
7 purchase totals =	$781.59		$839.4241	$839.42	$839.45	$839.50