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	$50.60	9.720%	$55.5183	$55.52	$55.50	$55.50
Purchase #2	$82.39	8.653%	$89.5192	$89.52	$89.50	$89.50
Purchase #3	$61.79	6.667%	$65.9095	$65.91	$65.90	$65.90
Purchase #4	$120.89	3.799%	$125.4826	$125.48	$125.50	$125.50
Purchase #5	$194.61	8.669%	$211.4807	$211.48	$211.50	$211.50
Purchase #6	$124.69	5.314%	$131.316	$131.32	$131.30	$131.30
Purchase #7	$99.90	9.152%	$109.0428	$109.04	$109.05	$109.00
7 purchase totals =	$734.87		$788.2691	$788.27	$788.25	$788.20