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	$117.74	12.355%	$132.2868	$132.29	$132.30	$132.30
Purchase #2	$179.46	6.399%	$190.9436	$190.94	$190.95	$190.90
Purchase #3	$52.75	13.812%	$60.0358	$60.04	$60.05	$60.00
Purchase #4	$200.48	9.654%	$219.8343	$219.83	$219.85	$219.80
Purchase #5	$37.53	11.621%	$41.8914	$41.89	$41.90	$41.90
Purchase #6	$215.64	11.634%	$240.7276	$240.73	$240.75	$240.70
Purchase #7	$57.27	3.280%	$59.1485	$59.15	$59.15	$59.10
7 purchase totals =	$860.87		$944.8680	$944.87	$944.95	$944.70