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	$31.49	11.617%	$35.1482	$35.15	$35.15	$35.10
Purchase #2	$128.91	9.769%	$141.5032	$141.50	$141.50	$141.50
Purchase #3	$108.44	6.809%	$115.8237	$115.82	$115.80	$115.80
Purchase #4	$147.79	7.142%	$158.3452	$158.35	$158.35	$158.30
Purchase #5	$163.46	9.175%	$178.4575	$178.46	$178.45	$178.50
Purchase #6	$246.29	7.688%	$265.2248	$265.22	$265.20	$265.20
Purchase #7	$98.37	11.194%	$109.3815	$109.38	$109.40	$109.40
7 purchase totals =	$924.75		$1,003.8841	$1,003.88	$1,003.85	$1,003.80