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	$88.33	10.813%	$97.8811	$97.88	$97.90	$97.90
Purchase #2	$31.50	9.457%	$34.479	$34.48	$34.50	$34.50
Purchase #3	$5.91	7.649%	$6.3621	$6.36	$6.35	$6.40
Purchase #4	$89.28	11.849%	$99.8588	$99.86	$99.85	$99.90
Purchase #5	$113.84	9.426%	$124.5706	$124.57	$124.55	$124.60
Purchase #6	$210.41	9.743%	$230.9102	$230.91	$230.90	$230.90
Purchase #7	$80.52	11.627%	$89.8821	$89.88	$89.90	$89.90
7 purchase totals =	$619.79		$683.9439	$683.94	$683.95	$684.10