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	$110.56	4.447%	$115.4766	$115.48	$115.50	$115.50
Purchase #2	$51.51	5.498%	$54.342	$54.34	$54.35	$54.30
Purchase #3	$190.96	6.383%	$203.149	$203.15	$203.15	$203.10
Purchase #4	$81.96	8.629%	$89.0323	$89.03	$89.05	$89.00
Purchase #5	$141.50	9.342%	$154.7189	$154.72	$154.70	$154.70
Purchase #6	$130.92	7.180%	$140.3201	$140.32	$140.30	$140.30
Purchase #7	$214.38	3.716%	$222.3464	$222.35	$222.35	$222.30
7 purchase totals =	$921.79		$979.3853	$979.39	$979.40	$979.20