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	$170.36	6.105%	$180.7605	$180.76	$180.75	$180.80
Purchase #2	$167.25	9.135%	$182.5283	$182.53	$182.55	$182.50
Purchase #3	$125.31	4.765%	$131.281	$131.28	$131.30	$131.30
Purchase #4	$38.94	5.199%	$40.9645	$40.96	$40.95	$41.00
Purchase #5	$88.72	8.733%	$96.4679	$96.47	$96.45	$96.50
Purchase #6	$130.41	10.772%	$144.4578	$144.46	$144.45	$144.50
Purchase #7	$221.29	3.869%	$229.8517	$229.85	$229.85	$229.90
7 purchase totals =	$942.28		$1,006.3117	$1,006.31	$1,006.30	$1,006.50