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	$52.27	13.271%	$59.2068	$59.21	$59.20	$59.20
Purchase #2	$35.81	6.163%	$38.017	$38.02	$38.00	$38.00
Purchase #3	$60.83	3.474%	$62.9432	$62.94	$62.95	$62.90
Purchase #4	$188.28	11.459%	$209.855	$209.86	$209.85	$209.90
Purchase #5	$81.72	12.115%	$91.6204	$91.62	$91.60	$91.60
Purchase #6	$37.45	10.526%	$41.392	$41.39	$41.40	$41.40
Purchase #7	$46.63	4.282%	$48.6267	$48.63	$48.65	$48.60
7 purchase totals =	$502.99		$551.6611	$551.67	$551.65	$551.60