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	$125.27	13.856%	$142.6274	$142.63	$142.65	$142.60
Purchase #2	$179.46	12.446%	$201.7956	$201.80	$201.80	$201.80
Purchase #3	$131.97	5.362%	$139.0462	$139.05	$139.05	$139.00
Purchase #4	$148.37	7.662%	$159.7381	$159.74	$159.75	$159.70
Purchase #5	$173.29	13.283%	$196.3081	$196.31	$196.30	$196.30
Purchase #6	$136.82	11.723%	$152.8594	$152.86	$152.85	$152.90
Purchase #7	$46.31	10.308%	$51.0836	$51.08	$51.10	$51.10
7 purchase totals =	$941.49		$1,043.4584	$1,043.47	$1,043.50	$1,043.40