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	$192.63	6.842%	$205.8097	$205.81	$205.80	$205.80
Purchase #2	$99.51	10.319%	$109.7784	$109.78	$109.80	$109.80
Purchase #3	$112.61	10.752%	$124.7178	$124.72	$124.70	$124.70
Purchase #4	$38.96	11.315%	$43.3683	$43.37	$43.35	$43.40
Purchase #5	$105.66	12.368%	$118.728	$118.73	$118.75	$118.70
Purchase #6	$28.93	8.632%	$31.4272	$31.43	$31.45	$31.40
Purchase #7	$232.59	7.513%	$250.0645	$250.06	$250.05	$250.10
7 purchase totals =	$810.89		$883.8939	$883.90	$883.90	$883.90