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	$89.96	9.313%	$98.338	$98.34	$98.35	$98.30
Purchase #2	$174.76	12.175%	$196.037	$196.04	$196.05	$196.00
Purchase #3	$81.77	4.302%	$85.2877	$85.29	$85.30	$85.30
Purchase #4	$140.46	10.824%	$155.6634	$155.66	$155.65	$155.70
Purchase #5	$78.47	9.665%	$86.0541	$86.05	$86.05	$86.10
Purchase #6	$60.51	8.210%	$65.4779	$65.48	$65.50	$65.50
Purchase #7	$179.35	12.870%	$202.4323	$202.43	$202.45	$202.40
7 purchase totals =	$805.28		$889.2904	$889.29	$889.35	$889.30