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	$243.81	4.854%	$255.6445	$255.64	$255.65	$255.60
Purchase #2	$31.47	12.195%	$35.3078	$35.31	$35.30	$35.30
Purchase #3	$55.81	4.627%	$58.3923	$58.39	$58.40	$58.40
Purchase #4	$28.92	7.382%	$31.0549	$31.05	$31.05	$31.10
Purchase #5	$41.36	13.771%	$47.0557	$47.06	$47.05	$47.10
Purchase #6	$103.43	8.306%	$112.0209	$112.02	$112.00	$112.00
Purchase #7	$36.53	11.400%	$40.6944	$40.69	$40.70	$40.70
7 purchase totals =	$541.33		$580.1705	$580.16	$580.15	$580.20