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	$25.92	5.674%	$27.3907	$27.39	$27.40	$27.40
Purchase #2	$115.33	9.131%	$125.8608	$125.86	$125.85	$125.90
Purchase #3	$117.91	11.849%	$131.8812	$131.88	$131.90	$131.90
Purchase #4	$98.41	10.830%	$109.0678	$109.07	$109.05	$109.10
Purchase #5	$190.78	4.249%	$198.8862	$198.89	$198.90	$198.90
Purchase #6	$61.81	5.463%	$65.1867	$65.19	$65.20	$65.20
Purchase #7	$225.90	10.838%	$250.383	$250.38	$250.40	$250.40
7 purchase totals =	$836.06		$908.6564	$908.66	$908.70	$908.80