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	$177.57	6.423%	$188.9753	$188.98	$189.00	$189.00
Purchase #2	$76.51	7.595%	$82.3209	$82.32	$82.30	$82.30
Purchase #3	$38.43	4.155%	$40.0268	$40.03	$40.05	$40.00
Purchase #4	$136.87	12.306%	$153.7132	$153.71	$153.70	$153.70
Purchase #5	$218.44	12.837%	$246.4811	$246.48	$246.50	$246.50
Purchase #6	$94.81	4.856%	$99.414	$99.41	$99.40	$99.40
Purchase #7	$115.88	6.405%	$123.3021	$123.30	$123.30	$123.30
7 purchase totals =	$858.51		$934.2334	$934.23	$934.25	$934.20