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	$7.34	7.441%	$7.8862	$7.89	$7.90	$7.90
Purchase #2	$45.69	6.805%	$48.7992	$48.80	$48.80	$48.80
Purchase #3	$177.46	3.139%	$183.0305	$183.03	$183.05	$183.00
Purchase #4	$179.82	5.595%	$189.8809	$189.88	$189.90	$189.90
Purchase #5	$189.64	12.279%	$212.9259	$212.93	$212.95	$212.90
Purchase #6	$140.31	3.472%	$145.1816	$145.18	$145.20	$145.20
Purchase #7	$56.58	5.833%	$59.8803	$59.88	$59.90	$59.90
7 purchase totals =	$796.84		$847.5846	$847.59	$847.70	$847.60