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	$132.39	6.664%	$141.2125	$141.21	$141.20	$141.20
Purchase #2	$32.68	8.619%	$35.4967	$35.50	$35.50	$35.50
Purchase #3	$86.83	11.438%	$96.7616	$96.76	$96.75	$96.80
Purchase #4	$42.75	4.234%	$44.56	$44.56	$44.55	$44.60
Purchase #5	$123.34	3.215%	$127.3054	$127.31	$127.30	$127.30
Purchase #6	$70.36	11.306%	$78.3149	$78.31	$78.30	$78.30
Purchase #7	$106.52	8.804%	$115.898	$115.90	$115.90	$115.90
7 purchase totals =	$594.87		$639.5491	$639.55	$639.50	$639.60