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	$40.52	12.451%	$45.5651	$45.57	$45.55	$45.60
Purchase #2	$32.86	13.854%	$37.4124	$37.41	$37.40	$37.40
Purchase #3	$163.31	10.528%	$180.5033	$180.50	$180.50	$180.50
Purchase #4	$79.40	3.844%	$82.4521	$82.45	$82.45	$82.50
Purchase #5	$212.72	11.843%	$237.9124	$237.91	$237.90	$237.90
Purchase #6	$136.33	8.474%	$147.8826	$147.88	$147.90	$147.90
Purchase #7	$47.26	12.384%	$53.1127	$53.11	$53.10	$53.10
7 purchase totals =	$712.40		$784.8406	$784.83	$784.80	$784.90