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	$24.88	13.715%	$28.2923	$28.29	$28.30	$28.30
Purchase #2	$168.72	9.638%	$184.9812	$184.98	$185.00	$185.00
Purchase #3	$128.43	9.689%	$140.8736	$140.87	$140.85	$140.90
Purchase #4	$120.48	3.126%	$124.2462	$124.25	$124.25	$124.20
Purchase #5	$130.47	11.871%	$145.9581	$145.96	$145.95	$146.00
Purchase #6	$121.75	5.671%	$128.6544	$128.65	$128.65	$128.70
Purchase #7	$223.66	11.706%	$249.8416	$249.84	$249.85	$249.80
7 purchase totals =	$918.39		$1,002.8474	$1,002.84	$1,002.85	$1,002.90