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	$98.62	11.258%	$109.7226	$109.72	$109.70	$109.70
Purchase #2	$46.33	12.838%	$52.2778	$52.28	$52.30	$52.30
Purchase #3	$30.26	4.391%	$31.5887	$31.59	$31.60	$31.60
Purchase #4	$148.47	5.258%	$156.2766	$156.28	$156.30	$156.30
Purchase #5	$200.30	5.107%	$210.5293	$210.53	$210.55	$210.50
Purchase #6	$79.50	11.650%	$88.7618	$88.76	$88.75	$88.80
Purchase #7	$160.93	8.313%	$174.3081	$174.31	$174.30	$174.30
7 purchase totals =	$764.41		$823.4649	$823.47	$823.50	$823.50