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	$72.69	12.139%	$81.5138	$81.51	$81.50	$81.50
Purchase #2	$112.56	9.712%	$123.4918	$123.49	$123.50	$123.50
Purchase #3	$54.30	9.405%	$59.4069	$59.41	$59.40	$59.40
Purchase #4	$79.83	4.539%	$83.4535	$83.45	$83.45	$83.50
Purchase #5	$243.73	5.790%	$257.842	$257.84	$257.85	$257.80
Purchase #6	$162.47	12.816%	$183.2922	$183.29	$183.30	$183.30
Purchase #7	$123.32	9.115%	$134.5606	$134.56	$134.55	$134.60
7 purchase totals =	$848.90		$923.5608	$923.55	$923.55	$923.60