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	$34.27	10.262%	$37.7868	$37.79	$37.80	$37.80
Purchase #2	$182.73	3.690%	$189.4727	$189.47	$189.45	$189.50
Purchase #3	$35.38	11.319%	$39.3847	$39.38	$39.40	$39.40
Purchase #4	$6.39	6.626%	$6.8134	$6.81	$6.80	$6.80
Purchase #5	$85.77	3.427%	$88.7093	$88.71	$88.70	$88.70
Purchase #6	$39.46	3.804%	$40.9611	$40.96	$40.95	$41.00
Purchase #7	$171.27	6.467%	$182.346	$182.35	$182.35	$182.30
7 purchase totals =	$555.27		$585.4740	$585.47	$585.45	$585.50