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	$189.30	8.497%	$205.3848	$205.38	$205.40	$205.40
Purchase #2	$175.46	5.828%	$185.6858	$185.69	$185.70	$185.70
Purchase #3	$10.90	3.786%	$11.3127	$11.31	$11.30	$11.30
Purchase #4	$112.56	12.236%	$126.3328	$126.33	$126.35	$126.30
Purchase #5	$65.38	12.134%	$73.3132	$73.31	$73.30	$73.30
Purchase #6	$39.67	6.515%	$42.2545	$42.25	$42.25	$42.30
Purchase #7	$61.61	7.266%	$66.0866	$66.09	$66.10	$66.10
7 purchase totals =	$654.88		$710.3704	$710.36	$710.40	$710.40