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	$109.80	12.654%	$123.6941	$123.69	$123.70	$123.70
Purchase #2	$33.61	10.314%	$37.0765	$37.08	$37.10	$37.10
Purchase #3	$206.57	6.356%	$219.6996	$219.70	$219.70	$219.70
Purchase #4	$5.73	10.200%	$6.3145	$6.31	$6.30	$6.30
Purchase #5	$104.40	7.164%	$111.8792	$111.88	$111.90	$111.90
Purchase #6	$119.43	6.413%	$127.089	$127.09	$127.10	$127.10
Purchase #7	$31.55	13.711%	$35.8758	$35.88	$35.90	$35.90
7 purchase totals =	$611.09		$661.6287	$661.63	$661.70	$661.70