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	$170.45	4.612%	$178.3112	$178.31	$178.30	$178.30
Purchase #2	$24.62	13.225%	$27.876	$27.88	$27.90	$27.90
Purchase #3	$33.39	7.394%	$35.8589	$35.86	$35.85	$35.90
Purchase #4	$23.69	6.488%	$25.227	$25.23	$25.25	$25.20
Purchase #5	$109.31	13.168%	$123.7039	$123.70	$123.70	$123.70
Purchase #6	$39.73	10.425%	$43.8719	$43.87	$43.85	$43.90
Purchase #7	$157.46	10.542%	$174.0594	$174.06	$174.05	$174.10
7 purchase totals =	$558.65		$608.9083	$608.91	$608.90	$609.00