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	$57.25	4.526%	$59.8411	$59.84	$59.85	$59.80
Purchase #2	$147.34	13.641%	$167.4386	$167.44	$167.45	$167.40
Purchase #3	$147.37	6.148%	$156.4303	$156.43	$156.45	$156.40
Purchase #4	$103.96	8.364%	$112.6552	$112.66	$112.65	$112.70
Purchase #5	$201.51	11.585%	$224.8549	$224.85	$224.85	$224.90
Purchase #6	$127.97	8.869%	$139.3197	$139.32	$139.30	$139.30
Purchase #7	$191.93	13.502%	$217.8444	$217.84	$217.85	$217.80
7 purchase totals =	$977.33		$1,078.3842	$1,078.38	$1,078.40	$1,078.30