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	$66.71	4.806%	$69.9161	$69.92	$69.90	$69.90
Purchase #2	$177.44	11.759%	$198.3052	$198.31	$198.30	$198.30
Purchase #3	$169.64	11.598%	$189.3148	$189.31	$189.30	$189.30
Purchase #4	$250.43	11.273%	$278.661	$278.66	$278.65	$278.70
Purchase #5	$142.46	5.304%	$150.0161	$150.02	$150.00	$150.00
Purchase #6	$41.76	13.469%	$47.3847	$47.38	$47.40	$47.40
Purchase #7	$196.94	10.819%	$218.2469	$218.25	$218.25	$218.20
7 purchase totals =	$1,045.38		$1,151.8448	$1,151.85	$1,151.80	$1,151.80