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	$101.53	8.247%	$109.9032	$109.90	$109.90	$109.90
Purchase #2	$182.28	12.343%	$204.7788	$204.78	$204.80	$204.80
Purchase #3	$37.78	7.269%	$40.5262	$40.53	$40.55	$40.50
Purchase #4	$75.49	7.860%	$81.4235	$81.42	$81.40	$81.40
Purchase #5	$119.32	7.275%	$128.0005	$128.00	$128.00	$128.00
Purchase #6	$119.89	9.715%	$131.5373	$131.54	$131.55	$131.50
Purchase #7	$115.33	11.768%	$128.902	$128.90	$128.90	$128.90
7 purchase totals =	$751.62		$825.0715	$825.07	$825.10	$825.00