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	$90.97	12.167%	$102.0383	$102.04	$102.05	$102.00
Purchase #2	$23.30	6.285%	$24.7644	$24.76	$24.75	$24.80
Purchase #3	$187.71	4.478%	$196.1157	$196.12	$196.10	$196.10
Purchase #4	$94.95	4.535%	$99.256	$99.26	$99.25	$99.30
Purchase #5	$135.35	3.709%	$140.3701	$140.37	$140.35	$140.40
Purchase #6	$163.73	4.354%	$170.8588	$170.86	$170.85	$170.90
Purchase #7	$31.60	4.111%	$32.8991	$32.90	$32.90	$32.90
7 purchase totals =	$727.61		$766.3024	$766.31	$766.25	$766.40