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	$22.34	8.870%	$24.3216	$24.32	$24.30	$24.30
Purchase #2	$154.76	10.701%	$171.3209	$171.32	$171.30	$171.30
Purchase #3	$84.72	5.617%	$89.4787	$89.48	$89.50	$89.50
Purchase #4	$92.76	11.747%	$103.6565	$103.66	$103.65	$103.70
Purchase #5	$33.65	11.383%	$37.4804	$37.48	$37.50	$37.50
Purchase #6	$196.71	8.223%	$212.8855	$212.89	$212.90	$212.90
Purchase #7	$172.80	9.662%	$189.4959	$189.50	$189.50	$189.50
7 purchase totals =	$757.74		$828.6395	$828.65	$828.65	$828.70