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	$31.58	6.868%	$33.7489	$33.75	$33.75	$33.70
Purchase #2	$84.88	5.628%	$89.657	$89.66	$89.65	$89.70
Purchase #3	$158.96	9.386%	$173.88	$173.88	$173.90	$173.90
Purchase #4	$158.46	6.672%	$169.0325	$169.03	$169.05	$169.00
Purchase #5	$51.84	4.236%	$54.0359	$54.04	$54.05	$54.00
Purchase #6	$181.40	9.321%	$198.3083	$198.31	$198.30	$198.30
Purchase #7	$238.89	11.845%	$267.1865	$267.19	$267.20	$267.20
7 purchase totals =	$906.01		$985.8491	$985.86	$985.90	$985.80